Capitol Hill. Photo: Brendan Smialowski/AFP/Getty Images

A big part of the angst Republicans are expressing over Donald Trump’s presidential nomination is the fear that he’ll doom GOP candidates down ballot. In part, that reflects the reality that ticket-splitting has been declining steadily in recent presidential years. The GOP’s Senate majority is fragile because of a particularly bad landscape. But now even the 59-seat margin Paul Ryan commands in the House could be in peril, though that’s a more remote contingency.

Ace House-watcher David Wasserman of the Cook Political Report has a new analysis at FiveThirtyEight that weighs the odds of a Democratic takeover pretty carefully. The GOP majority in the House is entrenched, he explains, by factors that have little to do with the popularity of the two parties:

Democratic voters have never been more concentrated in big urban areas than they are now. In 2012, President Obama won by 126 electoral votes while carrying just 22 percent of America’s counties — even fewer than losing Democratic nominee Michael Dukakis’s 26 percent in 1988. That means Democrats are wasting more votes than ever in safe congressional districts they already hold … Republicans’ astounding state legislative gains in the 2010 midterms — the year before the decennial redistricting cycle — allowed them to redraw four times as many congressional districts as Democrats in 2011 and 2012, stretching their geographical edge even further. As a result, in 2012, Democrats won 51 percent of all major-party votes cast for House candidates but just 47 percent of all seats.

A third thumb on the scales for House Republicans is that Democrats did not anticipate the possibility of a presidential landslide, and thus did not recruit top-flight candidates in some districts that now look vulnerable. With candidate-qualifying windows having passed in 79 percent of districts, it’s too late to do anything about that in much of the country.

All in all, Wasserman estimates, Democrats would need something like an eight-point national popular-vote margin to put themselves into a position to achieve the 30-net-seat gains necessary to retake the House. That’s hardly unprecedented since Democrats matched that margin in 2006 and exceeded it (with 10.6 percent) in 2008 (the much-ballyhooed Republican landslides of 2010 and 2014 were based on 6.8 percent and 5.8 percent House popular-vote margins, respectively). And current polls certainly indicate that a win by that sort of margin at the top of the ticket by Hillary Clinton is entirely feasible. But Wasserman’s own ratings for Cook show only 26 Republican-held seats — along with seven Democratic seats — being competitive. A “wave” election would require that additional seats come into play. There’s also an argument that if the presidential race gets out of hand for Republicans, they could make an implicit or explicit “checks and balances” argument in congressional races. That is supposedly how the losing presidential party minimized down-ballot losses in the landslide years of 1972 and 1984. It’s unclear that would happen again in this straight-ticket-voting era, but it’s not inconceivable.



The Senate’s a different situation. Of the 34 seats up this November, Republicans are defending 24 and can only afford to lose 3 and hang on to control if Democrats retain the White House and thus the vice-president’s tie-breaking Senate vote. Seven Republican seats are in states Obama carried twice (no Democratic seats are in states carried by McCain or Romney). Looking at the races more closely, Cook’s ratings show seven Republican-held seats in competitive races, with just two among the Democratic-held seats. A Democratic wave could make several other Republicans vulnerable. And none of the factors that give Republicans an advantage in keeping control of the House are relevant to Senate races.

If anyone’s going to be privately hoping something disastrous happens to the Trump candidacy before he’s nominated in Cleveland, it should be Mitch McConnell. But for Paul Ryan, the time to panic likely won’t arise, if at all, before the leaves begin to turn.

