Now that acceptance is finally starting to set in about Trump's impending nomination, few are more worried than those who hope to maintain a Republican congressional majority. Political science time!
Coat-tails. Whichever party wins the White House tends to gain seats in the House and Senate. Why? There are a lot of possible explanations, but one of the more prominent explanations is that winning presidential candidates have "coat-tails" that congressional candidates can ride to victory. How does that work? There are a couple of possibilities. First, if one party has a particularly appealing presidential candidate, that might increase turnout among his party's voters. If those voters stay loyal to the party in congressional races, then congressional candidates benefit from the presidential candidate's coat-tails.
The other possibility is that an appealing presidential candidate brings in some "independent" voters. Lots of voters will claim to be independent. Most are lying. Anytime you see a poll showing that 1/3 or more of the electorate consists of "independent" voters, you can ignore that poll. It was done by people who don't read political science.
In political science, we measure partisanship with a "branching" method of questions. In the first stage, we ask respondents whether they classify themselves as Democrats, Republicans or independent. Among the partisans, we ask about the strength of their party identity. Among the "independents," we ask whether or not they lean towards one party. Most do. Only about 10% of the electorate are true independents.
But in a close election, that's enough to sway the outcome. If the independents lean towards one presidential candidate for some idiosyncratic reason, what do they do on down-ballot races? The easiest thing to do is to just stick with the party of their presidential vote. And that's what they tend to do, ceteris paribus.
So, whoever wins the White House tends to pick up seats in Congress.
There's a flip side, and that's what has so many Republicans terrified. While I have suggested in the past that we might be underestimating Donald Trump's general election prospects (see here, here, here, and here), the best guess right now is that he is a weak candidate. That cuts two ways.
First, turnout. Republicans hate Hillary. But however much they hate her, it pales in comparison to how Democrats feel about Trump. Trump has changed the rules of political dialog so much that we openly discuss comparisons to Hitler and Mussolini when discussing him. His rallies regularly turn violent. Trump could motivate non-white voters to turn out for Hillary in historic numbers. And plenty of Republicans are sufficiently leery of him that they may stay home. Yes, the Bernie people are claiming they won't vote for Hillary, but most are either liars or deluding themselves. They'll vote for Hillary because the alternative will be Donald Trump.
Then, there's the "independent" problem. Donald Trump's favorable/unfavorable numbers are abysmal with independents. Will that change? Maybe, but it's a steep hill to climb.
All of this spells trouble for Republican congressional candidates. Their best hope for salvation is a tanking economy. Short of that, they need to dissociate themselves from Trump. Remember that Republicans have a majority in both the House and Senate. Their main task is to play defensively, and as long as vulnerable incumbents can distance themselves from Trump, they can survive.
So here's what we might expect. A deal. Donald Trump is not exactly the kind of person who can take criticism. Of anything. From anyone. He is the most thin-skinned candidate in modern history. And that can work for the Republican congressional candidates! They can bash him, and then when Trump responds, Republican congressional candidates in tough races will tout Trump's hatred as points in their favor! The party will appear to be at war with itself, but everyone involved will understand that it is a shadow play.
I can't wait.
But time for another episode of weird stuff that could still cost Trump the nomination! For today's installment, Donald Trump slips on a banana peel while walking to the podium, hits his head, and in a concussion-altered state of mind, reveals that he once had an affair with... Bill Clinton. That's what the phone call was about...