Earlier this week, as he was preparing the most important speech of his life, Senator Jeff Flake spoke privately with an acquaintance about the unusual political situation in which he found himself. He said that his chances at reëlection in Arizona next year were grim. Flake, the most consistent critic of Donald Trump among Republican senators, had an approval rating in the state that, as Trump gleefully pointed out on Twitter on Wednesday morning, was less than twenty per cent. In a TV interview Wednesday morning, the day after Flake delivered a speech announcing his retirement from Congress, condemning Trump, and promising to use his remaining time in office speaking out against the President, he was blunt about his political prospects. “The bottom line is that, if I were to run a campaign that I could be proud of and where I didn’t have to cozy up to the President and his positions or his behavior, I could not win in a Republican primary,” Flake said.

Many other congressional Republicans find themselves in the same political circumstances: they are shackled to the President not because they love him but because Republican voters do. Trump is far more popular with Republican voters than is the G.O.P. Congress or the Republican Party as a whole. These are not normal intra-party ideological divisions. Crossing Trump in any way is tantamount to betrayal. “I am aware that a segment of my party believes that anything short of complete and unquestioning loyalty to a President who belongs to my party is unacceptable and suspect,” Flake said in his speech. Trump’s takeover of the G.O.P. is a popular one, and is enthusiastically supported by the Party’s grass roots. Flake’s view is that the only way for Republican dissidents to win back some support is to break their silence.

Flake’s speech on the Senate floor on Tuesday was not directed at Trump. It was directed at the senator’s fellow elected Republicans. Flake portrayed Trump as dangerously unfit to be President, but his more important point was about the Republican Party’s responsibility for the current disaster. The most important line of the speech was at the top, when he said, “It is time for our complicity and our accommodation of the unacceptable to end.”

A day later, not many Republicans have joined Flake, though his speech has been praised by liberals and members of the “Never Trump” faction within the G.O.P. But what if some Republicans did accept the challenge? What could they actually achieve? Flake’s speech was frustratingly vague about concrete actions that Republican officials should take to reverse or contain the danger he sees in Trump. “Ambition counteracts ambition,” Flake said, quoting James Madison’s description of how one branch of government must rise up to check the other. But, aside from speaking out, the details of G.O.P. resistance were fuzzy.

Flake did not mention, for example, whether moderate Republicans should block Trump’s legislative agenda, as occurred with health care. In the next few weeks, the fate of Trump’s tax-reform proposal will likely be decided by the votes of a handful of moderate Republicans in the Senate. If the measure passes, Trump will gain a long-delayed legislative victory, strengthening his Presidency—and his dominance of the Republican Party. If tax reform fails to pass, as the effort to dismantle Obamacare did, Trump’s Presidency will be weakened, and, potentially, his hold on the Party will suffer as well. So far, Flake, Senator Bob Corker, Senator John McCain, and other moderate Republicans in Congress have failed to specifically call for such steps. Instead, they talk of more modest opposition to Trump.

One prominent anti-Trump conservative involved in politics whom I talked to argued that simply speaking out is actually the key for Party leaders. “The most important thing that Flake, Corker, or McCain can do is simply speaking truth,” this person said. “That’s absolutely critical, because we have been operating in this environment where many Republicans in Congress have been participating in this gaslighting of Americans about the dangers of Donald Trump’s Presidency. And so we need our leaders to speak truth, and when our leaders speak truth people will follow.”

Mark Salter, a longtime friend and speechwriter for John McCain, agreed with that sentiment. “Continue to speak up, call out every big lie and every wrong act,” he said when asked what Flake Republicans could do. But he also added a more tangible list of actions: “Protect the Mueller investigation, use your committee assignments to work with Democrats to demand accountability and transparency from the Administration, acting all along with more graciousness, sincerity, and patriotism than Trump is capable of exhibiting.”

Tim Miller, a former spokesman for Jeb Bush, also noted that there was a lot that Republicans in Congress could do “to counter the negative effects of Trump,” such as pushing for “long-overdue constraints on the executive branch” to limit executive-order authority—an idea that was popular among conservatives when Obama was President. Miller said that the G.O.P., for example, could examine the President’s continued ability to wage war under the Authorization for Use of Military Force, which was enacted after the 9/11 attacks; another possibility would be to strengthen the rules governing ethical violations, including “ending the practice of government officials using taxpayer money to pay any organization that is owned by a family member.”

Miller also suggested that Republican senators act more like whistle-blowers, publicizing private information about the kind of erratic behavior that Corker has described witnessing. “I think the more tangible examples of what [Trump] is doing behind the scenes would've buttressed Corker’s argument that he is a danger,” Miller said.

Most of the actions, short of impeachment, amount to a Republican Congress that views itself as being more in opposition to the executive branch—in other words, acting similarly to how it would act if a Democrat were in power. “There are actually plenty of straightforward things to do in the form of what once would have been pretty routine oversight and accountability,” Bill Kristol, the founder of The Weekly Standard, said.

Republicans speaking out in the way Flake has, acting as a check on the White House, rather than collaborators, could mitigate the worst-case scenarios that Flake described on Tuesday. But, so far, the overwhelming majority of Republicans are declining to serve as Trump watchdogs. As Kristol noted, “one of the corruptions of the moment is that many Republicans in Congress have totally abdicated that responsibility.”