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Can A Democrat Really Win A Senate Race In Tennessee? Or Mississippi?!?!

Republicans don’t have a lot of exposure in the Senate this year — but they’re doing what they can to help Democrats make the most of it. The GOP entered this election cycle with only eight of their own seats up for grabs. Republican incumbents retired in three of those seats, however, and while Democrats don’t really stand a chance in Utah — where Mitt Romney will almost certainly succeed Orrin Hatch — the races to replace Sen. Jeff Flake in Arizona and Sen. Bob Corker in Tennessee are highly competitive.

In addition, Mississippi Sen. Thad Cochran’s early retirement this spring triggered a special election that will add to the Nov. 6 docket and that also gives Democrats a plausible chance at a pickup. Just how plausible? Read on. We’re covering each of these races — along with the Minnesota special election, the lone Democratic retirement of the cycle following Sen. Al Franken’s resignation — in today’s installment of POLLS vs. FUNDAMENTALS, the extremely dorky series of articles in which I evaluate the conflicting perspectives that polls and non-polling factors (“fundamentals”) provide on the Senate this year. In contrast to races featuring Democratic incumbents, where including fundamentals in our forecast generally helped Democrats, it helps Republicans in states such Mississippi and Tennessee:

A big gap between polls and fundamentals

Forecasted margin of victory or defeat in open-seat races and races with appointed incumbents

Republican’s forecasted margin of victory or defeat
Race Incumbent Fundamentals Adjusted Polls
Arizona -1.4 -3.8
Minnesota special Smith (D) -15.8 -8.2
Mississippi special Hyde-Smith (R) +13.1 +5.9*
Tennessee +13.8 -1.1
Utah +26.8 +32.5

*Mississippi will hold a special election on Nov. 6, with candidates from all parties listed on the same ballot. If no candidate gets a majority of the votes, a runoff between the top two vote-getters will be held on Nov. 27. In the table, Hyde-Smith’s 5.9-point advantage reflects her lead over Democrat Mike Espy in polls of their prospective runoff. Another Republican candidate, Chris McDaniel, trails Espy by 17.6 points in runoff polling. In polls of the nonpartisan blanket primary scheduled for Nov. 6, Republicans lead Democrats in aggregate by 20.1 points in our polling average.

But let’s start in Arizona, which is a more straightforward case (and first in alphabetical order). In contrast to the relatively complex fundamentals calculation that our model makes for races featuring incumbents, the one for open-seat races is more straightforward: It accounts for only state partisanship, the generic congressional ballot, candidate experience, fundraising and a variable indicating whether or not a candidate is undergoing a scandal. In Arizona, Democratic nominee Kyrsten Sinema and Republican Martha McSally are both current U.S. representatives, meaning that the experience variable is a tie. And neither is caught up in a scandal. So the questions are who’s raised more money and whether the blue lean of the generic ballot is enough to offset the red lean of Arizona.

And the answer is … an open-seat race in Arizona ought to be pretty damned close in a political climate like this one. Hillary Clinton lost Arizona by only 4 percentage points in 2016, but the state has been more Republican-leaning than that in the past, and it’s been more Republican in statewide races than in federal ones. (Our partisanship variable accounts for state legislature results as well as presidential voting.) Sinema has a slight lead in fundraising, however, so the fundamentals calculation tips the race ever-so-slightly toward her, projecting her to win by nearly 2 percentage points. Sinema currently leads by slightly more than that, 4 percentage points, in the polling average. Nonetheless, this is a good example of how races tend to gravitate toward the fundamentals: Sinema’s polling lead had averaged 7 or 8 points before McSally won a contentious GOP primary last month.

FiveThirtyEight Senate forecast update for Sept 20, 2018

FiveThirtyEight treats races featuring appointed incumbents (as opposed to elected incumbents) as tantamount to open-seat races, both because some of the variables we use to evaluate incumbents aren’t available in the case of appointees and because appointed incumbents don’t have a very good track record at winning re-election. As a case in point, the Minnesota and Mississippi special elections still have the potential to create headaches for Democrats and Republicans, respectively, as the appointed incumbents in those states (Sen. Tina Smith in Minnesota and Sen. Cindy Hyde-Smith in Mississippi) aren’t performing especially well in polls.

Even so, it’s probably too ambitious to think that Republicans will win the Minnesota special election given that elected Democratic incumbent Amy Klobuchar is poised to win by a landslide margin in Minnesota’s other Senate race; so-called double-barrel Senate elections (in which both of a state’s Senate seats are on the ballot in the same year) are almost always won by the same party. But whereas the fundamentals calculation projects Smith to win by 15 points — she’s raised more money and has held the higher elected office1 — Republican nominee Karin Housley has held Smith’s margin to the high single digits in most polls. It could be that the Housley name has a little extra currency in hockey-obsessed Minnesota (Housley’s husband, Phil Housley, is a member of the Hockey Hall of Fame and the current coach of the Buffalo Sabers). Still, Smith has about a 9 in 10 chance of winning — odds that Democrats ought to be reasonably happy with, considering the unpredictable race that they might have faced in 2020 if Franken had remained on the ballot.

The Mississippi special election is the most complicated race on the November ballot — and one of the hardest to forecast. If you take the polls there more at face value, it looks like an underrated opportunity for Democrats; based on fundamentals, however, it’s more of a long shot.

Here’s how it works. On Nov. 6, Mississippi will hold a nonpartisan blanket primary featuring multiple candidates from each party. If no one receives a majority of the vote, the top two finishers will advance to a runoff on Nov. 27. (Basically, this is the same thing that Louisiana does with its congressional races every year.) There are three major candidates in the race: Hyde-Smith, the appointed Republican incumbent; Chris McDaniel, the controversial tea party-backed Republican who nearly defeated Cochran in the GOP primary four years ago; and Mike Espy, an African-American Democrat who served as a U.S. representative in the 1980s and 1990s and then as Bill Clinton’s first Secretary of Agriculture. (There’s also a second Democrat, Tobey Bartee, but he has only about 2 percent of the vote in polls.)

Polls of the blanket primary show Espy and Hyde-Smith roughly tied for first with about 30 percent of the vote each, and McDaniel some ways behind in the high teens, with a substantial number of undecided voters. None of those numbers are too surprising; President Trump endorsed Hyde-Smith, although she was ahead of McDaniel even before the endorsement. So there’s likely to be a runoff and it’s likely to feature Espy against Hyde-Smith.

There’s also polling of potential runoff matchups, however, and in those polls, Espy does surprisingly well — at least as compared to how the fundamentals might expect him to do. On average, he trails Hyde-Smith by only about 6 percentage points in head-to-head polls and leads McDaniel in a potential runoff by about 18 points. So the Lite version of our model, which forecasts the runoff based on polls only, gives Espy a decent shot of beating Hyde-Smith (and assumes he’d crush McDaniel on the off-chance McDaniel made the runoff instead). The Classic and Deluxe versions, by contrast, which account for fundamentals, consider that Mississippi is a red state and that the two Republicans are likely to get significantly more votes combined than the two Democrats (Espy and Bartee) on Nov. 6, which is historically a good predictor of runoff results. Thus, they see Espy as a fairly heavy underdog against Hyde-Smith, and also think he could have a tough time with McDaniel despite leading him in polls.

Every scenario in the special Senate election in Mississippi

Probability of occurring, based on 50,000 simulations as of Sept. 19, 2018

Scenario Lite Classic Deluxe
Espy wins a majority on Nov. 6 5.4% 5.9% 6.2%
Espy beats Hyde-Smith in runoff 17.4 8.9 9.3
Espy beats McDaniel in runoff 0.6 0.4 0.5
Hyde-Smith wins a majority on Nov. 6 2.7 2.1 1.8
Hyde-Smith beats Espy in runoff 71.8 80.5 80.4
Hyde-Smith beats McDaniel in runoff 1.5 1.4 1.2
McDaniel wins a majority on Nov. 6 <0.1 <0.1 <0.1
McDaniel beats Espy in runoff <0.1 0.3 0.3
McDaniel beats Hyde-Smith in runoff 0.5 0.4 0.3

Needless to say, all of this is pretty complicated. We’re doing the best we can to model these possibilities based on data from past races in Louisiana, as well as from California and Washington state, which use a somewhat similar top-two format, but there’s inherently a fair amount of uncertainty here. The bet the fundamentals would place is simply that a runoff held three weeks after Election Day in a deep-red state like Mississippi — one that could possibly determine control of the Senate — is highly likely to favor Republicans. But polls of the runoff are more equivocal.

In comparison to Mississippi, there’s nothing especially tricky about Tennessee — it’s just a case where polls and fundamentals have totally different perspectives on the race. Polls show roughly a toss-up there between Democrat Phil Bredesen, the former governor, and Republican U.S. Rep. Marsha Blackburn. (If anything, Bredesen has just the slightest lead, as he tends to be doing better in the higher-quality surveys.) The fundamentals, by contrast, project a Republican win of 14 percentage points. Tennessee is very red, having voted for Trump by 26 points. Unlike some other Southern states, it’s also quite red in statewide elections; Republicans have a 28-5 advantage in the Tennessee Senate, for example. Blackburn has also slightly outraised Bredesen so far, making it among the only competitive Senate races where the GOP has the fundraising lead. The model does give Bredesen credit for being a former governor, but he has a lot going against him.

Rather than parse Tennessee itself any further, let’s instead see what has happened in the past when polls and fundamentals clash. In the chart below, I’ve listed Senate races since 1990 where there was at least a 10-point gap between the polls and the fundamentals with 60 days to go in the campaign, based on backtested results from the FiveThirtyEight model. I’ve limited the analysis to races deemed to be competitive by the Cook Political Report and where there was an adequate amount of polling. For example, the Indiana Senate race in 2016 meets all of those criteria; Democrat Evan Bayh, a former governor and senator, was well ahead in polls, but the fundamentals calculation regarded Republican Todd Young as the favorite. (Young eventually won handily.)

What happens when polls and fundamentals clash?

Competitive U.S. Senate races since 1990 featuring at least a 10-point gap between polls and fundamentals with 60 days until the election

Democratic Candidate’s Margin 60 Days Before Election
State Year Polling Average Fund-amentals Actual Result Fundamentals more accurate than polls? Race moved in direction of fundamentals?
IL 1990 +19.4 +7.1 +30.1
IL 1992 +34.2 +12.2 +10.2
CA 1994 +16.7 +0.9 +1.9
NJ 1994 +18.5 +5.2 +3.3
OH 1994 -17.9 -7.9 -14.2
SD 1996 -0.7 -13.7 +2.6
CA 1998 +0.6 +10.7 +10.0
IL 1998 -4.7 +10.2 -2.9
NY 2000 -0.0 +17.0 +12.3
TX 2002 -1.8 -16.5 -12.0
LA 2004 -20.0 +3.9 -21.7
NC 2004 +8.3 -9.1 -4.6
SD 2004 +3.2 +15.7 -1.2
MD 2006 +6.6 +21.3 +10.0
NJ 2006 -1.2 +19.9 +9.0
PA 2006 +8.1 -3.4 +17.4
TN 2006 -3.3 +12.4 -2.7
VA 2006 -1.4 -18.1 +0.4
WA 2006 +10.4 +24.1 +16.9
AK 2008 +2.5 -28.2 +1.2
VA 2008 +22.7 +5.7 +31.3
AR 2010 -27.8 +4.1 -21.0
NC 2010 -6.4 -17.1 -11.8
NV 2010 +1.8 +13.1 +5.7
CT 2012 -1.6 +23.0 +11.8
SD 2014 -13.7 -30.8 -20.9
GA 2016 -13.1 -24.3 -13.8
IN 2016 +9.9 -6.1 -9.7

Races are listed if: (i) They had at least a 10-point gap between polls and fundamentals with 60 days to go until the election; (ii) they were rated as competitive rather than “safe” by the Cook Political Report; (iii) they had an adequate amount of polling (equivalent to a cumulative polling weight of at least 2); and (iv) they did not feature a viable third-party candidate.

What happened in these races? Polls came closer to the final margin about two-thirds of the time (in 18 of 28 cases). So if you had to choose between polls and fundamentals, you’d pick polls. However, the race moved in the direction of the fundamentals three-quarters of the time (in 21 of 28 cases). That is, if the Republican was doing better according to the fundamentals analysis than according to the polls, the Republican tended to gain ground 75 percent of the time, and likewise for the Democrat.

So the best forecast comes from taking a blend of (mostly) polls and (some) fundamentals. Exactly how much our model weights each component depends on the amount of polling and the amount of time left until Election Day. Essentially, the fundamentals calculation is treated as the equivalent of 1 or 2 recent, high-quality polls. So if there are 10 or 15 recent polls of a state, the fundamentals calculation has little influence. In states such as North Dakota where polling is fairly sparse, they can have more sway.

What that means for Tennessee is that any poll showing Bredesen tied or ahead — and perhaps even behind by 1-2 percentage points — is good news for Bredesen, because the model expects the race to revert toward Blackburn based on the fundamentals. With every new poll, it weights the fundamentals less and less. With that said, Bredesen isn’t out of the woods yet; that Indiana race took a long time to tip toward Young in 2016 before he surged ahead on Election Day.

Finally, we come to Utah, where there isn’t much suspense: Romney is a massive favorite according to both polls and fundamentals, and the only real question is whether he’ll be a reliable vote for Trump or a thorn in the president’s side.

CLARIFICATION (Sept. 20, 2018, 1:35 p.m.): A previous version of this article gave the impression that former Sen. Al Franken would have been up for re-election this year had he not resigned. His seat would normally not be up for election again until 2020.


  1. Smith doesn’t get credit for being a senator in our model because it wasn’t an elected office; however, she was previously Minnesota’s lieutenant governor, whereas Republican nominee Karin Housley is a member of the state Senate.

Nate Silver is the founder and editor in chief of FiveThirtyEight.