For as long as Donald Trump has been president, the hope that a Congress controlled by his own party would hold him accountable for his corrupt, destabilizing conduct has felt tantalizingly close but loomed just out of reach.

The main impediment has been the consensus within the Republican Party in favor of ignoring Trump’s misdeeds. But the more important one has been a collective action problem discouraging Trump-skeptics within the House and Senate GOP conferences from banding together with Democrats for the good of the nation.

In the House, where the Republican majority is numerically substantial, and most members are safely gerrymandered enough to survive an anti-Trump electoral backlash, this collective action problem has always been insoluble. But in the Senate, where Republicans have a two vote majority, and members are accountable to the citizenries of entire states, the challenge seemed surmountable. Three senators. All it would take is three Republican senators to bring Trump to heel.

Three Republicans have now and then materialized situationally to deny Trump legislative victories—most famously when Sens. John McCain (R-AZ), Lisa Murkowski (R-AK), and Susan Collins (R-ME) aligned to save the Affordable Care Act—but only when Trump’s political fortunes and their own diverged.

For nine months partisan and careerist considerations have loomed large enough in Republican thinking to prevent three from forming a bloc, and prioritizing their concerns about Trump over the demands of party unity and re-election.

Until today.

On Tuesday, citing the toxic political environment Trump has created, Sen. Jeff Flake (R-AZ) announced he would not seek re-election, and, in astonishing Senate floor speech, rendered incredibly harsh moral judgment on Trump and his Republican colleagues who would let Trump subvert American democracy for a high-income tax cut. Colleagues like, say, this guy.

“At the end of the day” @SenBobCorker will vote for tax reform, @SpeakerRyan says. “Put this Twitter dispute aside.” https://t.co/2FUhpkHFef pic.twitter.com/41tel2VWJe

— This Week (@ThisWeekABC) October 24, 2017

Republicans may yet get their tax cuts, and Flake may yet vote for them. But by the standards he set for himself Tuesday afternoon, his top priority has just become saving the country from Trump, even at the expense of Republican policy priorities.

And what made Flake’s speech especially momentous is that McCain and he and Bob Corker make three.

Since he was diagnosed with terminal brain cancer earlier this year, McCain has struck an uncanny balance as a Trump critic between outright complicity and full-scale rebellion. He has intimated—through tweets and public comments, but mostly just tweets—that he wants cutting the legs out from under Trumpism to be his final act in public life.

.@nytimes: “McCain in Twilight” https://t.co/uEwSszUBPM

— John McCain (@SenJohnMcCain) October 22, 2017

Until this week, Corker was the only other Republican senator who had staked out similar territory. Corker is an influential member of the Republican conference, the chairman of the Senate Foreign Relations Committee, and, most importantly, not seeking reelection. Earlier this month, he called Trump unfit for high office and warned that the president’s antics might trigger World War III.

Tuesday morning, before Flake’s announcement, Corker reiterated these concerns. Trump reacted on Twitter, repeating lies he told when he and Corker first came to rhetorical blows. Corker responded by broadening his attack, calling Trump a liar, and a poor role model, and intimating that his decision to support Trump last year was a mistake.

But two avowed anti-Trump Republicans, liberated from the political consequences of undermining him, is only enough to make Vice President Mike Pence a busy man breaking ties in the Senate.

The addition of Flake to the group creates at least the potential to bring Trump’s broad-spectrum assault on American civic life to an abrupt end. Flake is a member of Corker’s Foreign Relations Committee, which would be an ideal staging ground for hearings on Trump’s threat to the global order. He also sits on the Judiciary Committee, where he can team with Democrats to investigate Trump’s corruption—including his efforts to compromise federal prosecutors with jurisdiction over him, his campaign, and his businesses. If he were so inclined, he could also prepare to challenge Trump for the Republican presidential nomination in 2020.

But these kinds of options were available to all three men before this week. The real advent of having three Republican senators nominally committed to saving the country from Trump is that they can hit Trump where it hurts. No tax cuts until Trump releases his tax returns? Together, McCain, Corker, and Flake can make that happen. Unless the Republican majority grows, they can leverage their decisive power over legislation and the confirmation process to practically whatever ends they desire.

Unfortunately nothing that’s happened in the Trump era should leave us expecting Republicans in Congress will be the ones who alter Trump’s course. But the arithmetic of the current Senate has flipped the onus on these senators. Or, more precisely, they’ve flipped the onus onto themselves. The inescapable logical, if nothing changes, is that the senators who masqueraded as saviors of the republic will be fingered as the ones who passively let it be destroyed.