When FiveThirtyEight
last issued a U.S. Senate forecast
— way back in July — we concluded the race for Senate control was a
toss-up. That was a little ahead of the conventional wisdom at the time,
which characterized the Democrats as vulnerable but more likely than
not to retain the chamber.
Our new forecast goes a half-step further: We think the
Republicans are now slight favorites to win at least six seats and
capture the chamber. The Democrats’ position has deteriorated somewhat
since last summer, with President Obama’s
approval ratings
down to 42 or 43 percent from an average of about 45 percent before.
Furthermore, as compared with 2010 or 2012, the GOP has done a better
job of recruiting credible candidates, with some exceptions.
As always, we encourage you to read this analysis with some
caution. Republicans have great opportunities in a number of states,
but only in West Virginia, South Dakota, Montana and Arkansas do we rate
the races as clearly leaning their way. Republicans will also have to
win at least two toss-up races, perhaps in Alaska, North Carolina or
Michigan, or to convert states such as New Hampshire into that category.
And they’ll have to avoid taking losses of their own in Georgia and
Kentucky, where the fundamentals favor them but recent polls show
extremely competitive races.
Since a number of you may be new to FiveThirtyEight, I’m
going to go into slightly more detail than usual in explaining how we
make these forecasts. You’re welcome to skip past this next section if
you’re more interested in the forecasts than in how we came to them.
An overview of our methodology
In contrast to the forecasts we’ll begin issuing sometime this summer, which are strictly algorithmic
based on our senate forecast model, these are done by hand. However, they’re based on an assessment of the same basic factors our algorithm uses:
The single best measure of the national political environment, in our view, is the
generic congressional ballot.
Right now, it shows a rough tie between Democrats and Republicans. That
stalemate likely reflects voters’ dislike for both Obama and the
Republican Party.
A tie on the generic ballot might not sound so bad for Democrats. But
it’s a misleading signal, for two reasons. First, most of the generic
ballot polls were conducted among registered voters. Those do not
reflect the turnout advantage the GOP is likely to have in November.
Especially in recent years, Democrats have come to rely on groups such
as racial minorities and young voters that turn out much more reliably
in presidential years than for the midterms. In 2010, the Republican
turnout advantage amounted to the
equivalent of 6 percentage points,
meaning a tie on the generic ballot among registered voters translated
into a six-point Republican lead among likely voters. The GOP’s edge
hadn’t been quite that large in past years. But if the “enthusiasm gap”
is as large this year as it was in 2010, Democrats will have a difficult
time keeping the Senate.
Democrats’ other problem is one of basic constitutional mathematics.
Senators are elected in six-year cycles, so the seats in play this year
were last contested in 2008,
an extraordinarily strong year for Democrats. Even a strictly neutral
political environment, or one that slightly favored Democrats, would
produce a drop-off relative to that baseline. And Democrats’ losses will
grow this year if voters go from modestly favoring Republicans to
strongly favoring them.
Incidentally, we prefer to look at aggregate measures of the national
environment, like the generic ballot and Obama’s approval ratings,
instead of piecemeal ones such as voters’ views of Obamacare. Certainly
the unpopularity of the Affordable Care Act — and its clumsy roll-out
late last year — contributes to Democrats’ problems. But it’s
hard to tell where Obamacare’s unpopularity ends and President Obama’s overall unpopularity begins. Voters’ views of the economy
also have ambiguous effects in midterm years, especially when control of government is already divided.
Candidate quality. The notion of “candidate quality” might sound awfully subjective, but there are sound statistical ways to assess it.
Fundraising totals, especially individual contributions, are a good indication of a candidate’s organizational strength. Various
systems
rate a candidate’s ideology on a left-right scale, based on her voting
record or public issue statements, and we can compare those ratings
against those of voters in her state. And candidates who have previously
held elected office tend to outperform inexperienced ones, controlling
for other factors.
State partisanship. As Dan Hopkins
wrote at FiveThirtyEight last week, races of all kinds have become more and more correlated with presidential results in recent years. So the
Partisan Voting Index (PVI),
which compares how a state voted in the past two presidential years
against the national popular vote, is also a useful tool for
congressional races. At this early point in the cycle, there’s reason to
be skeptical of races where the polls are out of step with how the
state usually votes; states often revert to their partisan mean once
more voters engage with the campaign.
Incumbency. Incumbents may be unpopular in the abstract, but
they still win the overwhelming majority of races.
Incumbency still represents an advantage in most cases, and sometimes a
significant one. We can spot the potential exceptions by looking at an
incumbent’s approval or favorability ratings.
Head-to-head polls. Head-to-head polls at this point
in the cycle have some predictive power if evaluated carefully. That
means taking care to see whether the poll was conducted among registered
or likely voters, and putting less emphasis on polls when one or both
candidates lack widespread name recognition. However, as my colleague
Harry Enten
has lamented,
many of the more important Senate races have rarely been polled this
year. Furthermore, much of the polling comes from firms such as
Rasmussen Reports and Public Policy Polling, which have
poor track records, employ
dubious methodologies,
or both. So the most appropriate use of polls at this stage is to see
whether they roughly match our assessment of the race based on the
fundamentals. Where there is a mismatch, it could indicate that the
polls are missing something, that our view of the fundamentals is
incorrect, or some of both — and it means there is more uncertainty in
the outlook for the state.
Overall forecast
In consideration of these factors, we assess the
probability of the Democratic or Republican candidate winning each seat.
Where the choice of candidates is uncertain — for instance, in a race
where a Democrat will face either a moderate, six-term incumbent U.S.
representative or a poorly-financed tea party upstart, depending on the
outcome of the Republican primary — the probabilities are meant to
reflect a weighted combination of the plausible match-ups. Our
assessment of the 36 races up for grabs this November is as follows:
One advantage of looking at the races on a probabilistic
basis is that we can simply sum the probabilities to come up with a
projection of how the new Senate will look. That method projects that
Republicans will finish with 51 seats,
a net gain of six from Democrats, and exactly as many as they need to
win control of the chamber. (Democrats will hold the Senate in the event
of a 50-50 split because of the tiebreaking vote of Vice President Joe
Biden.)
That represents an edge for Republicans, but not much of
one — and there are any number of paths by which they might get to 51
seats, or fail to do so. It might help to break the 36 races down into
six categories, based on the party which holds the seat now and its
likelihood of flipping to the other party.
Democrat-held seats likely to be picked up by Republicans (4): West Virginia, South Dakota, Montana, Arkansas
You’ll find that our characterization of the 36 races in most cases is very close to that issued by such forecasters as the
Cook Political Report and
Rothenberg Political Report.
We’re looking at the same sort of information they are, and they have
strong track records, so it’s natural there should be similarities.
One point of difference is that we’re much more pessimistic
about the Democrats’ chances in West Virginia, South Dakota and
Montana. These races have a lot in common, taking place in three red
states where longtime Democratic incumbents have retired.
We’re bullish on Republican chances in these states for
simple reasons. First, they’re red states. Second, we think the national
political environment modestly favors Republicans. Third, we think the
Republicans are poised to nominate equal or superior candidates in each
state. Fourth, our research suggests there is little or no carry-over
effect from incumbency once the incumbent himself retires. In West
Virginia, for instance, the retirement of Democrat Jay Rockefeller
provides little information about how the race will turn out in
November.
We give Republicans a 90 percent chance of winning West
Virginia, in fact. The state’s politics are a little more complicated
than might be apparent from presidential voting — Obama is
extraordinarily unpopular there, but a slim majority of the state’s
voters are still
registered as Democrats,
and Democrats hold the governorship and both branches of the state
legislature. But Republicans are poised to nominate an excellent
candidate in Rep. Shelley Moore Capito, and she has held leads of 6 to
17 percentage points in polls against the likely Democratic nominee,
Secretary of State Natalie Tennant.
We also give Republicans a 90 percent chance of winning
South Dakota. It’s a more straightforward case, except that the
presumptive Republican nominee, Gov. Mike Rounds, has been
caught up in a controversy over the state’s participation in the
EB-5 immigration visa program. To have much of a chance, Democrats will either need Rounds to lose the Republican primary or be significantly damaged by it.
Montana is slightly different in that Democrats technically
do have an incumbent, John E. Walsh, running for re-election there.
However, Walsh was appointed, not elected (he replaced Max Baucus in
February when Baucus was named United States Ambassador to China).
Appointed senators have a
poor historical track record;
from a predictive standpoint, it’s best to think of their races as open
seats, rather than incumbent defenses. Walsh trails the likely
Republican nominee, Rep. Steve Daines, by double digits in polling so
far. The race is likely to tighten; Montana is somewhere between a
purple state and a red one, and Walsh, who was elected as Montana’s
lieutenant governor in 2012, is a credible candidate. Still, we give
Republicans an 80 percent chance of flipping it.
The final race in this category is Arkansas, where
Democrats have a true incumbent, Sen. Mark Pryor, running. Pryor was
once so popular that he won without Republican opposition in 2008. But
Arkansas has become redder and redder, and Democratic Sen. Blanche
Lincoln’s 21-point loss to Republican John Boozman in 2010 demonstrates
that past popularity is no guarantee of future success for a Democrat
there. Furthermore, Republicans have a strong candidate in Rep. Tom
Cotton, who is ahead by an average of about five points in recent polls.
Pryor will be able to fight for his seat — he had $4.2 million in cash
on hand as of Dec. 31, compared to $2.2 million for Cotton. The polling
has returned inconsistent answers about Pryor’s approval and
favorability ratings, so it’s hard to say how deep a reservoir of
personal goodwill he will have to draw from. But the evidence points
toward him being the underdog.
Democrat-held seats that are toss-ups (4): Louisiana, North Carolina, Alaska, Michigan
For Republicans, the path of least resistance to a Senate
majority is winning West Virginia, South Dakota, Montana and Arkansas,
and then two of the four states in this category.
Louisiana, where the Democratic incumbent Mary Landrieu is
running, may be the easiest opportunity. Landrieu’s fundamentals are
similar in most respects to Pryor’s: Her fundraising has been fine, but
otherwise she’s running against the tide in what has become a very red
state, and her moderate overall voting record may be undermined by
her role in passing the Affordable Care Act
in 2010. The difference is that Landrieu’s most likely opponent, Rep.
Bill Cassidy, has yet to pull ahead in the polls, which instead show a
race that’s roughly tied.
In North Carolina, Democrat Kay Hagan is an example of a
candidate who could go in and out with the political tides. She was
elected in 2008 over Elizabeth Dole as the Obama campaign turned out
African Americans and college students throughout the state. But those
are precisely the voters who don’t always show up for midterms. Still,
Hagan could get a reprieve depending on Republicans’ choice of nominee.
Republicans have eight declared candidates for their May 6 primary who
range from Thom Tills, the speaker of the state House, to a variety of
activists and political amateurs.
Alaska might be the hardest race to forecast. The polling
there is often erratic. The state has voted Republican for president
every year since 1968, but its
independent streak sometimes translates differently in other races.
The Democratic incumbent, Mark Begich, might face an establishment
candidate in Daniel S. Sullivan, the former attorney general, or Mead
Treadwell, the lieutenant governor — or he could face Joe Miller, the
former judge and tea party activist who is unpopular beyond the
Republican base.
The race in Michigan differs from the others in this group:
It’s somewhere between purple and blue instead of red, and there’s no
incumbent, as Democratic Sen. Carl Levin is retiring. But Republicans
will have an excellent candidate in Terri Lynn Land, the former
secretary of state. She comes from the old guard of moderate Michigan
Republicans, instead of the tea party wing that might have preferred a
candidate like Rep. Justin Amash. The likely Democratic nominee, Rep.
Gary Peters, should win his primary without serious opposition, and he’s
kept pace with Land in fundraising. But we take the polls that show the
race as a toss-up at face value. The question is whether Michigan’s
modest blue lean is enough to overcome a modestly Republican-leaning
national climate.
Democrat-held seats that lean Democratic but with a plausible GOP pick-up (3): Colorado, Iowa, New Hampshire
Republicans have some backup options if they fail to win states such as North Carolina and Michigan.
The best one is Colorado. The GOP got the candidate of its choice in Rep. Cory Gardner,
who declared for the race last month.
That will prevent them from again nominating Ken Buck, the tea party
candidate who lost a winnable race in 2010. (Buck has withdrawn from
this year’s Senate race and decided to run for the U.S. House instead.)
By our measures, Gardner is a decent candidate rather than a great one.
He’ll start at a fundraising deficit to the Democratic incumbent, Mark
Udall, who had $4.7 million in cash on hand as of Dec. 31, and he comes
from a conservative district and has amassed a conservative voting
record that may or may not translate well in the Denver suburbs. But
Udall’s approval ratings only break even, and we give Republicans a 40
percent chance of winning his seat.
The other big recruiting news is in New Hampshire, where
Scott Brown, the former Massachusetts senator, has announced he’ll seek
the Republican nomination. But as Harry Enten
noted,
Brown isn’t terribly popular in New Hampshire, which has long had a
love-hate relationship with Massachusetts. Just as important, Jeanne
Shaheen, the Democratic incumbent, has enjoyed approval ratings that
would be good enough to get her re-elected. The political winds in New
Hampshire can shift quickly, which is why we’re not ruling out a
Republican win. But we don’t think Brown improves the GOP’s chances much
as compared with another credible candidate.
Iowa is also a political bellwether. Sen. Tom Harkin, the
Democrat, is retiring, which might seem to give Republicans even or
better odds in a Republican-leaning national environment. But Democrats
have a substantial edge in candidate quality. Rep. Bruce Braley, the
presumptive nominee, has a fairly moderate voting record and $2.6
million in cash on hand. Meanwhile, Republicans have yet to coalesce
around one of several inexperienced candidates. Perhaps like the one in
New Hampshire, therefore, this race could swing Republican if the
Democrats’ national position deteriorates further; Braley would hold the
seat for them in an election held today.
Democrat-held seats likely or almost certain to be retained by Democrats (10): Minnesota, Oregon, New Jersey, Virginia, Hawaii (special election), Massachusetts, Illinois, New Mexico, Delaware, Rhode Island
Minnesota might seem vulnerable for Democrats. Sen. Al
Franken won his seat only after a months-long recount in 2008, and he’s
amassed the liberal voting record you’d expect of him. But Franken’s
approval ratings
are pretty good and he raises plenty of money from liberals around the
country. So far, he has deterred a credible Republican challenger from
entering the race.
In Oregon, Democratic incumbent Jeff Merkley has middling
approval ratings. But the state has become quite blue, and the
Republican roster there is weak; in 2010, the GOP nominated
inexperienced candidates in both the Senate and gubernatorial races. It
doesn’t look like they’ll nominate a strong candidate this year, either.
Their chances of victory depend on the electoral climate becoming
catastrophic for Democrats.
The other eight races on this list are likely to hold for
Democrats even in worst-case scenarios. Republicans have sometimes
talked up their opportunity in Virginia, where the former chairman of
the Republican National Committee, Ed Gillespie, is running. Ordinarily,
we’d snark about party hacks overrating the chances of one of their
brethren winning office, but Virginia just elected Terry McAuliffe as
its governor. However, Democratic incumbent Mark Warner maintains high
approval ratings, and he’d likely hold the seat even against a strong
opponent.
Republican-held seats that lean Republican but where Democratic pick-up is possible (2): Georgia, Kentucky
Republican paths to take over the Senate are complicated slightly by their need to defend two seats of their own.
The higher-profile problem is in Kentucky, where Sen. Mitch
McConnell, the Republican minority leader, has poor approval ratings,
and Democrats will nominate a charismatic candidate in Alison Lundergan
Grimes, the secretary of state.
Grimes has run about even with McConnell in polls since she declared
her candidacy in July. But McConnell will have all the financial
resources he could want — he had $10.9 million as of Dec. 31 — along
with Obama’s unpopularity in Kentucky to undermine Grimes. His path to
survival could resemble that of the Democratic leader, Harry Reid, who
prevailed in Nevada in 2010 with similarly poor approval ratings after a
brutal campaign. We give McConnell a 75 percent chance of holding the
seat. I’ll concede that I’m curious to see what our algorithmic
forecasts do with this race once they’re up and running.
Georgia might be the slightly better opportunity for
Democrats. The Republican primary, to be held May 20, has been a mess in
the polling, with any of five different GOP candidates near the top of
the race depending on the survey. Their prospects range from Secretary
of State Karen Handel, who might be the strongest general-election
nominee, to Reps. Phil Gingrey and Paul Broun, who have amassed
conservative enough voting records that they might turn off swing voters
even in red Georgia. Democrats are almost certain to nominate Michelle
Nunn, the daughter of former U.S. Sen. Sam Nunn, who has run even with
or slightly ahead of the Republicans in scant polling so far.
Ordinarily, we are skeptical of candidates who lack previous experience
in elected office, but those from famous political families don’t have
the same name-recognition deficit to overcome and can sometimes tap into
their families’ networks to raise funds and staff their campaigns.
Republican-held seats likely or almost certain to be retained by Republicans (13): Maine,
Mississippi, South Carolina (regular election), Nebraska, South
Carolina (special election), Texas, Tennessee, Oklahoma (special
election), Kansas, Oklahoma (regular election), Wyoming, Alabama, Idaho
Thirteen other Republican-held seats will be contested in
November, but none looks like a viable opportunity for Democrats. The
moonshot for Democrats might be in Mississippi, where the Republican
incumbent, Thad Cochran, is vulnerable to a primary challenge and
Democrats have a good prospective nominee in former Rep. Travis
Childers. Still, as Harry Enten explained,
it’s hard for any Democrat to get to 50 percent of the vote in Mississippi.
A wide range of outcomes
We’ve sometimes seen people take our race ratings and run
Monte Carlo simulations
based upon them, which assume that the outcome of each race is
independent from the others. But that’s a dubious assumption, especially
so far out from the election. Instead, the full-fledged version of our
ratings assumes that the error in the forecasts is somewhat correlated
from state to state.
In plain language: sometimes one party wins most or all of
the competitive races. If we had conducted this exercise at this point
in the 2006, 2008 or 2012 campaigns, that party would have been the
Democrats. In 2010, it would have been the Republicans. There are still
more than seven months for news events to intervene and affect the
national climate.
There are 10 races that each party has at least a 25
percent chance of winning, according to our ratings. If Republicans were
to win all of them, they would gain a net of 11 seats from Democrats,
which would give them a 56-44 majority in the new Senate. If Democrats
were to sweep, they would lose a net of just one seat and hold a 54-46
majority.
So our forecast might be thought of as a Republican gain of
six seats — plus or minus five. The balance has shifted slightly toward
the GOP. But it wouldn’t take much for it to revert to the Democrats,
nor for this year to develop into a Republican rout along the lines of
2010.
