This long-term shift toward nationalized congressional elections decided largely by attitudes about the president is affecting contests both in the places where Trump is popular and in those where he’s disliked. That means the party most satisfied with next month’s results may be the one with the most candidates who succeed at swimming against that current: Democrats who find ways to win in Trump country and Republicans who hold on in the major metropolitan areas moving away from him. At this point, pollsters in both parties don’t expect to find many examples on either side. “It’s going to be tough for both,” says Mark Mellman, a Democratic pollster. Bolger concurs: “It’s possible that both are disappointed.”
The correlation between attitudes about the president and voting choices in congressional elections has been increasing over the past generation. In a recent paper examining long-term survey data, Gary Jacobson, a University of California at San Diego political scientist who specializes in Congress, found that the congruence between voters’ assessments of the president and whether they supported his party’s candidate in House and Senate contests ticked up in the 1980s and 1990s before rising more rapidly in midterm elections during this century.
Exit polls now track a powerful connection between attitudes toward the president and votes in both House and Senate elections. In the past three midterm elections—2006, 2010, and 2014—exit polls found that 84 to 87 percent of voters who approved of the president’s performance voted for his party’s candidates in House elections. Simultaneously, 82 to 84 percent of those who disapproved of the president’s performance voted against his party’s House candidates. Since most voters in each election disapproved of the president’s performance, his party suffered substantial House losses each time.
The general assumption among political operatives is that because senators are better known than House members and raise more money to create an independent identity through television advertising, it’s easier for them to resist this trend. And in almost every election cycle, there are senators who conspicuously notch victories in states that lean the other way in their presidential preference. For instance, two of the most threatened Democratic senators in this election—Claire McCaskill in Missouri and Joe Donnelly in Indiana—won in 2012 while their states were voting for Mitt Romney over Barack Obama, largely because each benefited from a deeply flawed opponent.
The general trend, though, is for Senate races also to increasingly align with attitudes toward the president. In 2006, Republicans won six of 10 Senate contests in states where exit polls put George W. Bush’s approval rating at 46 percent or higher, but lost 19 of 20 in states where he stood at 45 percent or less. In 2010, Democrats won nine of the 10 Senate races in states where Obama stood at 48 percent or higher, but only two of the 15 where he had fallen to 47 percent or less. (Joe Manchin, facing a tough reelection fight again this year in West Virginia, was one of those two.) In 2014, Democrats lost Senate races in 14 of the 15 states where Obama’s approval rating slipped to 42 percent or less. In the 2016 election, every Senate race was decided the same way as the presidential contest in that state. “In the ’80s and ’90s, you could point to so many individual senators who bucked the partisan trends in their states to win, and you can’t do that as much anymore,” says Bolger.