The nightmare possibility for the party is that swing voters punish the party because of Mr. Trump, the anti-Trump Republicans stay at home and Mr. Trump’s base casts a ballot for him and then leaves the polls. Under those conditions, Senate races in places like Pennsylvania and North Carolina could fall to Democrats, while Senate and House races in places like Missouri, Arizona and Kansas could move to the center of the battlefield.
Already, Republicans view Mr. Trump’s sharp downturn in the presidential race as having jeopardized their majorities in Congress. A poll published on Tuesday by NBC News and The Wall Street Journal found Mr. Trump trailing Mrs. Clinton by nine percentage points nationally and drawing just 37 percent of the vote. No major-party nominee since World War II has received a smaller share of the vote. But in an illustration of the bind Republicans are in, the poll found that three-fourths of Republicans believed their candidates should stay loyal to Mr. Trump.George H.W. Bush only received 37% in 1992. And it is instructive to note that Democrats actually lost seats in the House that election, while breaking even in the Senate. Bill was a lot more popular in 1992 than Hillary is today. So I think these "perfect storm" prognostications by The New York Times are more fanciful agitprop than political math.
Hillary will win because of the gender gap. But she is not popular, and her coattails will barely cover her ass.