A bit of trivia often used to illustrate the growing prevalence of straight-ticket voting is that in 2016, the party of all 34 winning Senate candidates also carried their states in the presidential election. In other words, there were no down-ballot “crossover” wins in Senate races.
It’s less well-known that the number of crossover House wins actually increased from 26 in 2012 to 35 in 2016, thought that’s still a low number historically (there were 124 in 1976).
Straight-ticket voting helped Republicans win the “trifecta” in 2016, seizing the White House while maintaining control of both Houses of Congress (they did lose six net House seats, while narrowly winning the national House popular vote). Given the incredibly polarized atmosphere of 2020, will the two presidential candidates have the kind of down-ballot coattails they seemed to have in 2016? And is the effect strong enough that it should influence party resource targeting to maximize down-ballot rewards?
At FiveThirtyEight, Geoffrey Skelley examines the research on the “coattail effect,” and suggests it’s real, and it’s also not the same thing as straight-party voting, though it is generally accompanied by it:
Experts argue that where we really see the coattail effect is in turnout among a party’s base. “The way [the top of the ticket is] going to benefit the down-ticket candidates the most is by getting members of that party to show up to vote,” said [Marc] Meredith. This is especially true in our polarized era that has high rates of straight-ticket voting. “For every 10 partisans to get out to vote for a presidential candidate, you’re probably getting eight or nine of them voting for the [same party’s] House candidate,” added [James] Campbell.
So logically, you’d see the strongest coattail effect in states where the presidential campaigns are most active. That’s worth keeping in mind when you consider that seven competitive Senate races are in six states that are or could become presidential battlegrounds (Michigan, Arizona, Georgia, North Carolina, Colorado, and Maine). So if, for example, the Biden and Trump campaigns are trying to decide whether to concentrate resources in this or that battleground state, they might take a longer look at Georgia than might otherwise be the case, since that state has two reasonably competitive Senate races. For that matter, Iowa may have four competitive House races to go along with a competitive Senate race. It all has to go into the calculus of where to buy ads, focus get-out-the-vote efforts, and plan events (assuming we are having those at some point in this pandemic year).
In some recent presidential elections, a very different down-ballot effect has appeared, at least among high-information and relatively nonpartisan voters: a balancing effect aimed at keeping any one party from excessive power:
Looking at elections from 1948 to 2012, political scientist Robert Erikson of Columbia University found that if a presidential candidate was heavily favored to win, highly engaged, moderate voters often cast House votes for the other party — an “ideological hedge” of sorts. It’s true that only a relatively small number of voters do this, and split-ticket voting for president and Congress has generally declined in recent years, but enough voters still do this that it can make a difference in House races.
Indeed, that may have happened in 2016 in a number of suburban House districts where Clinton won but GOP House candidates eked out victories (though many of them perished in 2018) — another effect of the very widespread belief that Clinton had the presidential contest in the bag until Election Night. It would be surprising if that dynamic prevailed again in 2020; even if the presidential race doesn’t look very close when voters begin to vote, the 2016 experience should strongly mitigate against assuming it’s over.
There are two Senate races where unusually strong Democratic candidates are running in deep-red states: Alabama incumbent Doug Jones and Montana governor Steve Bullock. Most political analysts think the coattail effect (Trump carried the state by 27 points in 2016) will make it nearly impossible for Jones to win unless the kind of intra-Republican turmoil that helped him survive a 2017 special election recurs. In Montana, the expectation that Trump’s coattails (he won that state by 20 points four years ago) will carry Republican incumbent Steve Daines safely across the finish line is complicated by the fact that Bullock won gubernatorial elections in 2012 and 2016, despite large GOP wins in the presidential race. Generally speaking, gubernatorial candidates are less susceptible to presidential coattails because their races often revolve around a different set of issues. So Daines remains the favorite, unless Trump’s margin in the state dwindles significantly. Similarly, while the possibility of a Kris Kobach nomination has given Democrats hope that an open Senate seat in Kansas might come into play, it’s another state Trump won by 20 points in 2016. Any kind of coattails at all might save even a candidate as flawed as Kobach.
But while coattails may exist for both presidential candidates in a very close race, it’s important to remember that Democrats have significantly higher odds of flipping the three net Senate seats they’d need (along with a presidential win) for control than Republicans have of flipping the 17 net House seats they need for control of that chamber. While a continuation of divided control of Washington remains entirely possible, if there’s a new trifecta it is very likely to be on Joe Biden’s coattails.