That kind of mass Republican defection has grown harder, not easier, to imagine. It’s grown harder because the last six months have demonstrated that GOP voters will stick with Trump despite his lunacy, and punish those Republican politicians who do not.

Among Republicans, Trump’s approval rating has held remarkably steady. The week Mueller was named, according to Gallup, Trump’s GOP support stood at 84 percent. In the days after Donald Trump Jr. was revealed to have written, “I love it” in response to a Russian offer of dirt on Hillary Clinton, it reached 87 percent. In Gallup’s last poll, taken in late November, it was 81 percent. Trump’s approval rating among Republicans has not dipped below 79 percent since he took office. None of the revelations from Mueller’s investigation—nor any of the other outrageous things Trump has done—has significantly undermined his support among the GOP rank and file.

The GOP senators who have challenged Trump, by contrast, have seen their support among Republican voters crash. In July, Arizona Senator Jeff Flake’s brave and honorable book was excerpted in Politico as “My Party Is in Denial About Donald Trump.” Trump retaliated, of course. And by October, a Morning Consult poll found that Arizona Republicans disapproved of Flake by 13 points. That month, he declined to run for reelection. The other GOP senator to most frontally challenge Trump has been Tennessee’s Bob Corker, who in a series of interviews in October, accused him of “debasing” the presidency and warned that he could lead America into World War III. The result: A similar collapse of support. As The Washington Post’s Aaron Blake has noted, Tennessee Republicans approved of Corker in February by 40 points. By the end of October, they disapproved of him by 12 points. Not surprisingly, Corker isn’t running for reelection either.

Could Mueller or some enterprising journalist uncover revelations so epic that they shake Trump’s hold on the GOP, and give Republican senators cover to support his removal? It’s unlikely. After all, the vast majority of Alabama Republicans still support Roy Moore. Most conservatives consume pro-Trump media, which will downplay or distort virtually anything Mueller or the mainstream press discovers. And the more aggressively Democrats push for Trump’s removal, the easier it will be for Breitbart and Sean Hannity to rally Republicans against a “left-wing coup.”

Democrats did something similar during the battle over Bill Clinton’s impeachment. By September 1998, more than 100 newspapers—including USA Today, the Chicago Tribune and the Philadelphia Inquirer—had called on him to step down. That month, CNN reported that Democratic “lawmakers are privately telling top White House aides that the president should consider resigning.”

But Clinton survived, largely because Democratic voters stuck by him. If anything, the Republican-led impeachment effort boosted his popularity among his party’s base. When Newsweek first broke the news of Clinton’s relationship with Monica Lewinsky in January 1998, according to Gallup, his approval rating among Democrats was 86 percent. After he admitted to lying about the affair in August, it hit 89 percent. By the time the Senate voted on impeachment in February 1999, it hit 91 percent.

The last decade has shown that you can get big things through Congress with the support of only one party. In 2009, Democrats passed a stimulus bill and Obamacare with no help from the GOP. Last week on tax cuts, Republicans did the reverse. But removing a president requires bipartisanship. And in this ultra-partisan age, that means removing a president is virtually impossible, even when he’s Donald Trump.

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