It feels like our democracy is hurtling toward a cliff. Trump is hinting that he might try to shut down Robert Mueller, the special prosecutor investigating whether his campaign colluded with Russia. If he did so, he’d be following in the footsteps of Richard Nixon, who forced the resignation of both his attorney general and his deputy attorney general before he found a Justice Department lackey—Robert Bork—willing to fire special prosecutor Archibald Cox. Yet Nixon’s power grab was constrained by a Democratic Congress. Trump has a Republican one. And if the only thing standing between the American public and outright authoritarianism is the civic integrity of congressional Republicans, we’re in an inconceivably dangerous place.

Various resistance groups have started contingency planning for what happens if Trump attempts to kill the Mueller probe. “No one’s going to do anything prematurely, or accept the idea that Trump is going to or can fire Mueller,” said Fred Wertheimer, founder of the government watchdog group Democracy 21. “But if that should happen, or if he issues pardons, then a large number of groups that have been coordinating their efforts are going to be ready to help take the issue to the country and the Congress.”

If news breaks that Trump has forced Mueller out, Wertheimer believes that “the country will explode.” For the resistance, the trick is making sure the explosion is sustained. “That means people in the streets, demonstrations, marches, folks coming to Washington, a massive lobbying effort in Congress,” he said.

Yet everything keeps coming back to pushing a Congress that has so far been supine before the president and often hostile to dissenting constituents. “If Trump were to fire Mueller, that is to me the straw that breaks the camel’s back,” Democratic Congressman Ted Lieu told me. “I think at that point you’re going to have large numbers of Republicans saying we need to start impeachment proceedings.”

This should be true, but I’m not sure it is. Certainly, Republicans have been expressing horror about the idea of Mueller’s firing. Friday, Congressman Mike McCaul, chairman of the House Homeland Security Committee, told Andrea Mitchell that if Trump moves against Mueller, it would lead to a “tremendous backlash response” from House Republicans. Still, over the past six months, Republicans have shown themselves adept at tolerating the intolerable; one longtime Republican operative recently told me that no one has any idea where the tipping point might be.

For now, absent a plan to overthrow an illegitimate government, members of the resistance have no choice but to work through their representatives. “If Congress does nothing, that means the pressure ratchets up more in response,” said Lisa Gilbert, vice president of legislative affairs at Public Citizen. “We’re hoping to do everything we can to make that impossible.” Looking back to Nixon, she said, “There was a moment when it became too much and pressure had to be relieved, and Congress had to act. Similarly to the special counsel being appointed in the first place in this situation. We wouldn’t have thought that the Trump administration would do that, but they had to do something. In every situation, there’s a moment when it’s just too much.”

And if that moment doesn’t come for House Republicans, the midterms will become a referendum on impeachment. “We do need the people to rise up and say this is so wrong, we need to have a complete change in course of our government, or we need to remove the president,” Lieu said. “I go back to Lincoln’s famous quote: ‘Public sentiment is everything.’”

Of course, if public sentiment were everything, Trump wouldn’t be president. Yet it’s striking, in talking to progressive activists, how optimistic they feel about eventually meeting Trump’s challenge to our democracy. Wertheimer lived through Watergate, and says the feeling is familiar. “For many people it felt terrifying,” he said. “People were afraid, they were furious, they were upset, they were angry, but they were not about to take it.”