It is often said that the U.S. Presidency is a relatively weak office—but that is a contingent statement. To prevent the President from gaining too much power, or abusing that power, the Founding Fathers divided authority among the different branches of government, and established some fundamental governing principles. These are the fabled checks and balances, arranged, as James Bryce, the British jurist, noted in his venerable 1888 tome, “The American Commonwealth,” to “restrain any one department from tyranny.”

But the checks and balances only work if each of Bryce’s departments agrees to play its allotted role. A President enabled by a spineless and supine Congress that fails to exercise its oversight powers isn’t a weak executive at all: he is a potential despot. Using his authority to hire and fire federal officials, he can rapidly remake the government to his own design, appointing loyalists to key positions, eliminating potential threats, and undermining alternative repositories of power.

Authoritarian leaders in foreign countries seize and maintain power this way. And, despite his bungling start, this is the project that Donald Trump appears to have embarked upon. Since the end of January, he has appointed one of his closest political allies, Jeff Sessions, to run the Justice Department; fired an acting Attorney General, Sally Yates, who had warned the White House that the national-security adviser was compromised; and axed forty-six U.S. Attorneys, one of whom, Preet Bharara, had jurisdiction over Trump’s business empire. Now the head of the F.B.I., James Comey, has been ousted, at a time when the agency is conducting an investigation into possible collusion between Trump’s election campaign and the Russian government.

And how has the Republican-controlled Congress responded? On Wednesday, speaking on the Senate floor, Mitch McConnell, the Senate Majority Leader, spoke about Comey’s firing while barely mentioning Trump. Instead, he recalled how Democrats had vociferously criticized Comey’s actions during the F.B.I.’s investigation into Hillary Clinton’s e-mails. He also claimed, falsely, that it was not Trump but Rod Rosenstein, the Deputy Attorney General, who removed Comey. McConnell curtly dismissed calls for the appointment of an independent prosecutor to take over the Russia investigation, saying that such a move would “only serve to impede the current work being done” on Capitol Hill, where committees in the House and Senate are also looking into Russia’s meddling in the election.

This reaction was in keeping with McConnell’s record. He has long demonstrated an unwillingness to look beyond partisan concerns, and his wife, Elaine Chao, serves as Trump’s Transportation Secretary. Paul Ryan, the House Speaker, however, once had (and perhaps still has) pretensions to be a statesman. Last October, after the release of the “Access Hollywood” video in which Trump boasted of grabbing women by the genitals, Ryan said that he would no longer defend Trump, who was then the Republican nominee. But since Election Day those words have turned out to be empty. “The President lost patience, and I think people in the Justice Department lost confidence in Director Comey himself,” Ryan told Fox News on Wednesday evening. He also said, “It is entirely within the President’s role and authority to relieve him, and that’s what he did.”

Perhaps it was fanciful to expect anything more from the G.O.P.’s leaders. After Trump won in November, they made a political deal with him. As long as he pursues their legislative agenda—gutting Obamacare and other government programs, axing regulations, cutting taxes on the wealthy—they are likely to stick with him under almost any circumstances, even as their pact gets ever more Faustian.

It was a bit more surprising to see some of the supposedly more independent-minded Republicans also slavishly spouting the White House line. On Tuesday night, Senator Susan Collins, of Maine, issued a statement that said, “Any suggestion that today’s announcement is somehow an effort to stop the FBI’s investigation of Russia’s attempt to influence the election last fall is misplaced.” Senator Lindsey Graham, of South Carolina, who has criticized Trump on other matters, said, “I believe a fresh start will serve the F.B.I. and the nation well.”

With the Democrats largely powerless, much depends on the dozen or so Republican senators who have expressed some qualms about Comey’s dismissal. None have backed the calls for an independent prosecutor to take over the Russian probe. But some of them did make the obvious link between the timing of Comey’s firing and the progress of the investigation, and they also demanded a fuller explanation.

Senator Lisa Murkowski, of Alaska, said, “Whether or not you are a supporter of Mr. James Comey’s actions as F.B.I. director, the timing of his firing —in the middle of an investigation into Russia’s interference in our election—is serious cause for concern.” Senator Ben Sasse, of Nebraska, called the timing of the dismissal “very troubling.” And Senator Shelley Moore Capito, of West Virginia, said, “I think we need to find out what’s happened and why.”

Statements like these indicate unease at Trump’s action and an intention to wait and see what emerges over the next few days. On Thursday, various news accounts said that Comey had been seeking to expand the Russia probe in the days before he was canned. The Wall Street Journal reported that associates of Comey were denying Trump’s claim that he told the President he wasn’t a target of the investigation. A Washington Post story about the firing said, “Trump was angry that Comey would not support his baseless claim that President Barack Obama had his campaign offices wiretapped . . . And he fumed that Comey was giving too much attention to the Russia probe and not enough to investigating leaks to journalists.”

The official version of why Trump acted—that he had decided Comey’s handling of the Clinton investigation was botched—is risible. As a more convincing narrative emerges, we can only hope that enough Republicans find the conscience and guts to stand up to Trump and lay down a marker. If they don’t, the consequences could be catastrophic.

Anybody who thinks the President will stop here hasn’t been paying attention. It would be flattering Trump’s capacity for advance planning to claim that he has a blueprint for abrogating the Constitution and seizing more power. But throughout his career he has exhibited a willingness to push things as far as he can on an opportunistic basis, running roughshod over competitors, business partners, ordinary people, rules, and regulations. As the history of the high-pressure sales scam that was Trump University showed, he only backs off when he is forced to.

Trump’s willingness to say and do things that most people would shy away from because they are constrained by social norms, or ethics, helped carry him to where he is today. “He gets an idea in his head and just says, ‘Do it,’ ” Barbara Res, a former vice-president in the Trump Organization, told Politico’s Michael Kruse. Artie Nusbaum, one of the managers of the construction firm that built Trump Tower, said, “This is who he is. No morals, no nothing. He does what he does.” That is who the Republicans are enabling. Until they stop doing it, they will be complicit in the erosion of American democracy.