Speaking today at a White House press conference, President Obama directly addressed the issue of Donald Trump, and Republicans’ support for him. “The Republican nominee is unfit to serve as president,” he said, in his strongest words to date. “The notion that he would attack a Gold Star family that made such extraordinary sacrifices on behalf of our country, the fact that he doesn’t appear to have basic knowledge of critical issues in Europe, the Middle East, in Asia, means that he’s woefully unprepared to do this job.”

Obama also questioned Republicans for sticking by Trump: “There has to be a point at which you say, ‘Enough.'”

That’s not all. Today, Rep. Richard Hanna of New York became the first Republican member of Congress to announce that he’s going to vote for Hillary Clinton in the fall. In an interview and op-ed published on Syracuse.com, Hanna expressed outrage at Trump’s battle with the Khan family, and said, “I think Trump is a national embarrassment. Is he really the guy you want to have the nuclear codes?”

Now that someone has gone first, is this going to open the floodgates to a wave of Republican officeholders endorsing Clinton?

To answer that question, we have to keep in mind that politicians are human. They have sincere beliefs, and they sometimes get angry or offended or disgusted, and those emotions can affect their decisions. That being said, if you want to figure out what they’re going to do, the best strategy is to look at the incentives they have before them. What will they gain and lose from each course of action? If you know that, you can predict pretty accurately what they’ll decide.

The most important thing to know about Richard Hanna is not that he’s a relative moderate within his party, or that he comes from a swing district (both of which are true). It’s that he’s retiring. So he doesn’t have to worry about the political consequences of his actions, and he can do whatever he wants.

How about Republicans who are concerned about their political futures? Before we look at the politics, let’s think about policy. I’ve argued for months that even if Republicans find Trump personally repellent, supporting him is perfectly rational from where they sit. Sure, he might be an erratic ignoramus with no coherent ideological beliefs. But he’ll sign pretty much every bill they send him: upper-income tax cuts, repeal of the Affordable Care Act, rollback of environmental regulations, restrictions on abortion, you name it. He’ll nominate conservative judges, particularly to the Supreme Court. The executive branch will be staffed with the same people who would serve in almost any Republican administration. That’s a lot to be gained if you’re a conservative. It’s notable that the group of Republicans most clearly opposed to Trump — the foreign policy community — are those who care less about those domestic questions and who worry that his impulsiveness and stupidity would directly affect the things they do care about.

Other Republicans can justify their support by saying, “Sure, I’m appalled when he does things like get in a fight with a Gold Star family. But does that really make a difference to what will happen over the next four years, when there’s so much else at stake?”

Here's what politicians from both parties are saying about the row between Donald Trump and a man whose son was killed serving in Iraq. (Monica Akhtar/The Washington Post)

Of course, that’s predicated on the assumption, or at least the possibility, that he’ll actually win. The greater the chances that he’ll lose, the greater the incentive you’ll have to reject him, so you can look like you were on the right side of history. If he loses big and the whole party winds up agreeing that Trump was a disaster, you’ll be in a better position if you can say you were right about him all along (which seems to be Ted Cruz’s strategy in setting himself up for a 2020 run).

But it’s also important to remember that with just a few exceptions, the entire GOP has become complicit in Trump’s takeover of their party. There are a couple of officeholders like Sen. Ben Sasse who spoke out against Trump early and forcefully. But since everybody else has signed on to one degree or another, there won’t be a lot of people within the party who are eager to start a civil war targeting those who supported their failed nominee. Almost everyone has been soiled by Trump.

The last consideration is this: If you go all the way like Hanna did and say you’ll support Hillary Clinton, where does that put you in 2017 — or more pointedly, in 2018, when members of the House are up for re-election? If Clinton wins, she will be the focus of all of Republicans’ hatred, contempt, and rage. They’ve already decided that she ought to be imprisoned. Even if she succeeds in reaching across the aisle to pass a bill here and there, Republicans will be spending every day arguing that she’s a vile witch who is responsible for everything that goes wrong anywhere in the world. I wouldn’t be surprised if they start drawing up articles of impeachment the day after she takes office.

If that’s the prevailing thinking within the GOP, then anyone who supported her will be an immediate target, even if she’s doing a good job and is reasonably popular with the country as a whole. That will be true of almost any Republican member of Congress, most of whom represent extremely conservative districts where Clinton will always be loathed. Trump may become yet more despicable between now and November, but even if he loses in a landslide, there’s nothing to be gained for a Republican by supporting Clinton — except a primary challenge from the right in 2018.

Right now there are basically four positions you can take on Trump if you’re a Republican:

  1. I support him, no matter what he says or does.
  2. I support him, but I don’t like that latest thing he said. This is the position held by Paul Ryan, Mitch McConnell, and many vulnerable incumbents like Sen. Kelly Ayotte and Sen. John McCain.
  3. I can’t support him, but I won’t support Clinton. This is the position taken by a number of moderate Republicans like Sen. Mark Kirk or Rep. Charlie Dent, along with some conservatives like Sasse and Mitt Romney.
  4. I not only don’t support him, I think Hillary Clinton ought to win in order to prevent him from becoming president. So far, Richard Hanna is the most prominent Republican to take this position.

Given the incentives Republicans have, we aren’t going to see many — maybe not any — moving to position Number Four. What we may well see as the campaign goes on, particularly if Trump falls further in the polls or finds new disgusting things to say and people to offend, is a significant movement from Number Two to Number Three, with more Republicans saying they’ve decided not to vote for Trump but instead to write in “Zombie Ronald Reagan” or something similar on their ballots. The question is whether that can save them at the polls, or whether they’re forever stained by their association with their party’s nominee.