If you don't belong to the Republican Party, the reasons for the new impeachment inquiry against President Trump are pretty clear cut: The president used the power of his office to pressure Ukraine's president to investigate and undermine one of his political rivals. That is wrong, a misdeed aimed at the very heart of the democratic process.

GOP leaders, naturally, responded by declaring that the real villain here is House Speaker Nancy Pelosi (D-Calif.), who called for the impeachment inquiry.

"So I think at the end of the day the speaker owes an apology to this nation," House Minority Leader Kevin McCarthy (R-Calif.) told reporters, "and I think it's even a question why she should stay in her job."

Curiously, McCarthy once famously confided to other GOP leaders that he thought Trump was in the pocket of Russian President Vladimir Putin. So why is he sticking his neck out for the president now? Indeed, why are most Republicans vowing to stand by Trump?

The short answer is that many of those Republicans believe opposing Trump will bring an end to their own careers, even if he is clearly in the wrong. The longer answer involves the infamous Access Hollywood tape.

That tape — which featured Trump making crude remarks about groping women — emerged about one month before the 2016 presidential election, and for a couple of days it appeared the backlash might finish Trump's candidacy. More than two dozen elected Republicans, including then-House Speaker Paul Ryan, quickly disavowed him or sought to replace him on the presidential ticket so that the party could move on. Even McCarthy was sharply critical of Trump, and warned that he "must make a full and unqualified apology."

The Republican leadership failed. Trump survived. Today, the party has largely been remade in his image. The incident taught Republicans that opposing Trump is a difficult and dangerous game. This is why they are so steadfast in their devotion to him, even as the president faces impeachment.

While Trump demands loyalty among his party members, he himself is rarely loyal to anyone. Attempting to use GOP relationships as leverage in order to nudge him into doing the right thing is impossible. During the Access Hollywood controversy, for example, it became clear to GOP officials fairly quickly that it would do no good to ask Trump to quit the race "for the good of the party."

As Politico reporter Tim Alberta recounts in his recent book, American Carnage: "Even some of the people endorsing such an ultimatum knew how silly it sounded. Trump cared nothing for the party; he had not belonged to it until signing his name to a piece of paper a year earlier."

Trump will never quit in the face of shame or pressure. Most likely he will double down. But just because he cannot be persuaded to step down, though, doesn't mean he cannot be forced out.

Indeed, many senior Republicans wanted to kick Trump off the presidential ticket back in 2016 after the tape was released. They were unable to, however: The GOP simply didn't have a process in place to remove a presidential candidate from the ballot against his will. As the controversy mounted, Alberta reports in the book, then-Republican National Committee Chairman Reince Priebus fielded "scores" of calls from prominent party members — "congressmen and senators, governors, donors, activists, and his own RNC members" — urging him to replace Trump atop the ticket.

"Priebus had to explain — to Ryan and to everyone else — that there was no mechanism for removing Trump," Alberta writes.

The rules also give Trump an edge during the impeachment process. It takes two-thirds of the Senate to vote to convict a president on the impeachment charges and remove that person from office. Republicans control the Senate, of course, and it's unlikely enough members will defect to make removing Trump possible. He won't go if the Senate won't force him out.

And that leads us to anther reason GOP officials are so loyal to Trump: Their voters love him. It was the same during the 2016 controversy. In the first polls after the tape became public, just 12 percent of rank-and-file Republicans wanted to see Trump removed from the ticket. Even today, Trump remains popular with the party faithful. Elected Republicans, as a rule, don't want to test that popularity by risking their own careers — even if Trump is unmistakably and provably in the wrong.

All of this means that there are few incentives for leading Republicans to oppose the president. It has not gone unnoticed that the loudest in-party voices against him during the 2016 controversy — Ryan, Priebus — no longer hold official jobs in Washington, D.C. Republicans tried to kill Trump's candidacy that year and failed. They will be much more cautious about making a second attempt.

It is possible the dynamic could change. Richard Nixon commanded the loyalty of Republicans until he didn't. And there are already signs that the Ukraine scandal might be bigger and worse than what we've already been told. But GOP leaders, if they act at all, will probably wait until they can be assured that it is Trump — not them — who will lose a job when the process is over.

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