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Just four years ago, the GOP’s leaders were almost uniformly reacting to Trump with horror. Today, Republican officeholders have made their calculation: They will either go down with President Donald Trump, or they will rise with him.

The GOP has in recent years been the more disciplined of America’s two major political parties, and although Trump likes to complain that his fellow Republicans aren’t as regimented as Democrats, the Senate impeachment trial shows otherwise.

We won’t know until this evening exactly how many Republicans will vote in favor of witnesses in the Senate—whether Mitt Romney and Susan Collins will be joined by Lisa Murkowski, in other words—but Majority Leader Mitch McConnell is now confident he has the votes to defeat witnesses. That vote is now just a way station on the road to Trump’s inevitable acquittal, which could come as soon as tonight.

That outcome will be the latest evidence of Trump’s unshakable hold over the Republican Party. If there were a group of GOP officials who might still resist the president’s style and approach, it might have been found in the Senate. Senators are temperamentally institutional, jealous of their own prerogatives, and comparatively insulated from the most intense electoral demands on other officeholders. In the end, though, GOP senators got in line.

Trump still doesn’t inspire the same level of cultish devotion among Republican officeholders as he does among Republican voters. Time and again during his political career, he has said or done something that has appalled, mortified, or scandalized GOP politicians: There was the Access Hollywood tape in October 2016. There was the week in May 2017 when he fired FBI Director James Comey, then shared classified material with Russian leaders. There was his obsequious appearance with Vladimir Putin in Helsinki in July 2018. Each time, the initial reaction has been horror and even condemnation from Republican officials, followed—within a few short days—by acquiescence and acceptance.

This happened twice during the impeachment drama. In the early stages of the scandal, Republicans criticized Trump’s call with Ukrainian President Volodymyr Zelensky. Senator Lindsey Graham said he’d be very disturbed if Trump had engaged in a quid pro quo. But eventually the GOP settled down, and Graham now says the quid pro quo is perfectly fine.

The second example arrived this week. After news of former National Security Adviser John Bolton’s book, which confirmed the factual case alleged by House Democrats, Republican senators seemed to be reeling. Senator Angus King, a Maine independent who caucuses with the Democrats, and is apparently very naive, predicted that as many as 10 Republicans would vote to hear witnesses. Reports said that McConnell didn’t have the votes to block witnesses. Now, of course, it seems obvious that witnesses are out, leaving things right where they were before the Bolton revelations.

Why is it that these moments bend but never break Republican support? This is politics, and the simplest answer is probably political. Vulnerable senators like Cory Gardner of Colorado and Martha McSally of Arizona are risking their seats by lining up behind Trump. Both face tough races in November. Gardner will likely run against the popular former governor John Hickenlooper. McSally lost an election last November, was appointed to fill another Senate seat, and is struggling against the Democratic challenger, Mark Kelly.

Yet it’s not clear that going against Trump would help either Gardner or McSally, and the opposite is more likely. Candidates occasionally try to run away from presidents of their own party who are unpopular in their state, and it almost never works. Such a maneuver is unlikely to win over Democrats and moderates who dislike Trump—especially for first-termers like Gardner and McSally, who don’t have a long-standing relationship with voters—while it might alienate Republican voters the senators desperately need to hold.

In 2010, for example, some moderate Democrats attempted to distance themselves from Barack Obama, and they were almost entirely swept out of office. Then again, other Democrats tried to stay close to Obama, and many of them were swept out of office too.

Running away from the president is even less likely to work in 2020 than it did in 2010. Not only is the election more nationalized than in previous years, but Trump himself is on the ballot. Although he is historically unpopular, Trump remains wildly popular with Republican voters—hence the bind for endangered senators. If Trump wins reelection, his coattails may save the Gardners and McSallys of the world, but if he is defeated, they’re probably doomed anyway.

While Gardner and McSally offer a particularly dramatic example, this simple political calculation explains the discipline within the Republican ranks: Trump is a fact of life, and if there’s little to gain from backing him, there is much to lose by breaking with him. This is true even for senators who are retiring and don’t plan to face voters again. Republicans who cross Trump risk harming their post-office career prospects, and they risk social ostracism, as Politico’s Tim Alberta notes.

What these calculations leave out is any consideration of the actual charges facing the president and what they mean for rule of law and the future of the American government. Perhaps some Republicans believe that Trump really did nothing wrong, but that hardly speaks well for their judgment, and it is difficult to imagine them feeling similarly about a Democratic president who did the same.

While few Republicans are willing to say so out loud—see above, on the benefits of breaking from Trump—many do seem bothered by his behavior. Some believe that Trump acted inappropriately but that his conduct doesn’t merit removal, the position taken by Senator Lamar Alexander of Tennessee yesterday, when he announced that he would not vote in favor of calling witnesses. But Alexander is retiring, and nearly 80 years old; his younger colleagues mostly don’t dare say that aloud.

Still, the brief, frantic reaction to the Bolton news this week shows that, contrary to what some critics would claim, the Republican Party hasn’t lost its moral sense. What it has lost is any inclination to let that moral sense weigh on its political decisions.

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