By the summer of 1974, it was clear to leading Republicans that Richard Nixon would not be able to survive Watergate. It fell to Republican leaders like Barry Goldwater, Senate Minority Leader Hugh Scott of Pennsylvania, and House Minority Leader John Rhodes of Arizona to tell the president that support among his partisans in congress had collapsed and his presidency was over. The secret White House tapes had been made public and Nixon’s criminal culpability was clear enough to lead once-supportive Republicans to abandon a president of their own party. This was a wrenching decision but it spoke to the political reality of the moment. Nixon would be forced from office because his allies concluded that they needed to abandon him to survive.

As you may have noticed, this isn’t 1974. Republicans—even some who had been critical of Donald Trump in an earlier day—are clinging to him tightly. They are condoning or joining efforts to discredit the probe into Russian hacking of the 2016 election, going so far as to elevate partisan attacks against the FBI and Justice Department over national security concerns. Remember when Republicans were the self-proclaimed “law and order” party that venerated the FBI? Not so much today. It’s kind of hard to respect the rule of law when you’re defending a president who disregards it.

The Russia investigation isn’t as far along as Watergate was in mid-’74, but there is plenty of evidence of Trump attempting to obstruct it—enough to support impeachment hearings tomorrow if Republicans wanted to throw Trump overboard. But they would rather enable his efforts to derail the investigation. What’s different? Watergate occurred at the start of a long period of Republican rule, when the party coalition was expanding and resilient. Today, Republicans are at the end of the line. Nixon was less than two years removed from a 49-state Electoral College sweep when he left office. And while the resignation of a president comes at tremendous cost to a political party (Republicans lost big in the congressional elections of 1974 and narrowly lost the presidency two years later), only six years would pass before Republicans stormed back and begin their long ascendency: 12 straight years and 20 of the next 28 controlling the White House, with enduring majorities in the Senate and eventually the House.

The Trump administration comes at the end of that long arc of dominance. Far from winning in a landslide like Nixon, the current White House occupant lost the popular vote by over three million. Republicans thus far have been able to stave off annihilation at the hands of a rapidly diversifying electorate behind voters that find in Trump a voice for their grievances and are ready to punish anyone who dares stand in his way. Congressional Republicans may not be afraid of Trump, who by traditional measures of public opinion is a very weak president, but they live in fear of his base, which they need to maintain their increasingly tenuous hold on power. So they are doing whatever it takes to prop him up, knowing that their political lifeline would vanish if they abandoned him.

This is a desperate moment for Republicans and it shows in their actions. Those who might argue that the party would be better off ditching Trump in favor of a more politically-minded and restrained Mike Pence do not grasp that the loyalty of Trump’s voters is not transferrable. Republicans cannot abandon Trump and expect to coast along with his understudy, especially after Trump makes Pence and every Republican who abandoned him the object of his rage. At the end of a regime cycle and on the wrong side of demographic trends, Republicans would come undone by Trump’s undoing, and they are unwilling to relinquish their status as the dominant force in American politics. It is what drives them above all else.

The dilemma for Republicans is the more they play to their base, the more they alienate everyone else. This has been their dilemma since the rise of Trumpism, but it is about to face a major test in November. A massive defeat at the polls could make some Republicans re-think their support of Trump, but that defeat would have to be resounding, its message unequivocal. The prospect of losing power through their association with Trump has to become greater than the prospect of holding power by embracing him. If the electorate makes it clear that continuing to support Trump is a road to oblivion, then Trump can be removed. But it’s going to require a tsunami that sweeps away Republican enablers, dislodging their grip on the national legislature and statehouses across the country, posing the credible threat that presidential-level turnout in 2020 will wash away the party for a generation. Anything less will just push Republicans closer to their base and embolden them to continue to defend Trump as their last, best way to maintain their power. That’s why the 2018 election is the most important of our lifetime.

This may not be 1974, but if Republicans are subjected to a catastrophic defeat up and down the ballot, next year just might be.