One thing House Speaker Paul Ryan was probably doing by announcing he was withholding his support of Donald Trump was giving some of his more vulnerable House members room to do the same. Because all of a sudden what didn't seem even remotely possible this cycle is no longer completely unthinkable (though still not likely). At the very least, some House seats could flip under the Trump Effect.
A number of Ryan's most vulnerable colleagues had already said much the same thing. Colorado Rep. Mike Coffman said Trump had a long way to go to earn his support. Reps. Rod Blum (Iowa) and John Katko (N.Y.) simply did not respond to requests for comment. Several congressional Republicans, like Michigan Rep. Mike Bishop, tempered statements that they would support the GOP nominee with criticism of how Trump has conducted his campaign.
The filibustering reflects a spot of rare agreement, for once this year, between Democrats and Republicans: Trump’s poll numbers are worse than any presidential nominee’s in history, but there is no evidence yet that Trump’s unpopularity is harming Republicans running for Congress down the ballot. Polling in the swing district of Rep. Lee Zeldin, a Long Island Republican who endorsed Trump this week, showed Trump leading Hillary Clinton there, Zeldin said.
Yet Republicans acknowledge that they've entered uncharted territory. The party is waiting nervously to see if Trump’s low numbers with women, Latinos and other groups stay confined to the presidential race or start affecting congressional campaigns, potentially putting their previously unassailable 30-seat majority in jeopardy.
Trump's victory this week, and the realization that there really is no way to stop him with a contested convention or anything else, has hit Republicans hard. Pollsters, too, have been so focused on the primary that the impact of Trump down ballot in the general election hasn’t been really tested. His massive unpopularity with women and people of color and people with functioning brains has been pretty clear, as has how he could harm Republicans in state-wide races. It's been assumed for months now that his nomination would expand the Senate map for Democrats, and we're just at the beginning of finding out how true that will be for the House, too.
It's enough of a threat that plenty of House Republicans—including Paul Ryan—are taking it seriously.