But, as Trump's numbers — nationally and in key swing states — continue to tank, a creeping fear has taken root within the Republican establishment that maybe, just maybe, a landslide loss at the top of the ticket could cost the party not only the upper chamber of Congress but the lower one, too.

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A tweetstorm this morning by Robert Blizzard, a Republican pollster with the firm Public Opinion Strategies, won't make queasy GOPers feel any better. Here are his eight tweets in order:

First, a very broad but important point from Blizzard's tweets: It is VERY hard for a House candidate — whether incumbent or challenger — to run significantly ahead or behind the top of the ticket in a presidential year. The presidential race is so all-encompassing for voters — and House members/candidates typically so little known — that how the top of the ticket goes heavily dictates the results of House races. That's true even in cases where the House incumbent specifically tries to run away from the top of the ticket; voters tend not to differentiate all that much — if they are voting against the Republican at the top of the ticket, they usually do the same down-ballot. It's why political waves occur — and why we call them waves.

Now to the specific numbers behind Blizzard's math. His calculation is that the best an endangered incumbent can hope for is to run five points ahead of Trump. So, how many Republican seats might that include?

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The Cook Political Report lists 45 Republican seats and 11 Democratic ones as potentially competitive in November. Let's focus in on those 45 Republican seats.

Of the 45, 40 remain largely intact from the 2011 national redistricting process. (Florida engaged in a mid-decade redraw.) For those 40 seats, we can overlay the Cook Report's Partisan Voting Index (PVI) in an attempt to compare apples to apples. (The PVI ranks every district against every other district based on presidential performance.) Of the 40 GOP-held districts, 36 have a PVI of R+5 or lower, meaning that they are five points (or less) more Republican at the presidential level than all of the other districts in the country.

If Republicans lost all 36 of those seats with a PVI of R +5 or lower — and Democrats held all 11 of their contested seats — Democrats have the House majority. By six seats. Twenty-seven of those 40 seats have a PVI of R+3 or lower. Win those 27 and Democrats need to pick up only three seats among the slightly more Republican-friendly districts to win the majority.

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I still don't think a Democratic House majority is the likely outcome on Nov. 8. Republicans have to rely on the fact that so many of the congressional line redraws created districts where people are Republicans and are going to vote Republican — even if Trump is leading the ticket.

But if you trust Blizzard's calculations — and I do — it suggests that if the bottom drops out on Trump, which appears to be happening as I type, there are a good number of Republican-held House districts that could suddenly collapse with him.