Senator Bob Corker, a Republican of Tennessee, deserves credit for saying in public this evening to The New York Times what most prominent Republicans have known and many have said (in careful privacy) over the past two years.

Namely: that Donald Trump is irrational, ill-informed, impulsive, unfit for command, and increasingly a danger to the country and the world. The man who has ultimate authority over the world’s most powerful military, including its nuclear weaponry, is recklessly issuing threats to North Korea and others that set the nation “on the path to World War III,” according to Corker—who, for the record, is chairman of the Senate Foreign Relations Committee. “I know for a fact that every single day at the White House, it’s a situation of trying to contain him,” he told Jonathan Martin and Mark Landler of the Times.

This situation is not normal. It is not safe. And the group which for now has a monopoly on legislative and investigative power in Washington, Corker’s own Republican Party, has an obligation to the country’s past and its future to do something about it. Talk is better than nothing, but action is what counts.

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I am hardly the best-sourced figure on partisan politics in general and Republican officialdom in particular—and I’ve been away from Washington most of this year. But even I have heard, first-hand, from Republican senators, representatives, and other dignitaries that they view Donald Trump as a menace in his current role. It’s not (just) that they disagree with some of what he does. It’s that they consider him intellectually unaware of the cliffs toward which he is steering the country, and temperamentally unable to exercise anything like mature judgment. In these and other ways, including his personal and financial ethics, they know that he is outside the range of suitability to hold this job.

Should I have outed the people who said these things—or should the countless other press people who have heard similar views? No: Reporters do have to keep confidences, and I conveyed the substance of this case as best I could during the Trump Time Capsule series through the election. Moreover, it’s not clear that “concerns” like these would have changed anyone’s mind. During the campaign, most of Trump’s fallen rivals blasted him in exceptional terms—before truckling to support him against Hillary Clinton. One of the most remarkable illustrations was Senator Ted Cruz’s extended denunciation of Trump as a “pathological liar” just before Trump clinched the nomination. Of course Cruz turned around to support him in the general election and has cast nearly all his Senate votes (94 percent) in alignment with Trump. Meanwhile, it’s not even the lead news of the week that Trump’s own secretary of state has half-heartedly non-denied Stephanie Ruhle’s report on NBC that he called Trump a “fucking moron.”

Now that Bob Corker, one-time supporter of Trump, has taken the commendable step of going public, what’s next?

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For reporters, there is a logical extension from the opening Corker has given. Get Mitch McConnell, get Paul Ryan, get John Thune and John Barrasso and John Cornyn, get Kevin McCarthy, get every Republican in a position of responsibility to answer: Do you agree with your colleague that Donald Trump is a danger to the country and the world? Who’s right here: Your comrade who is the veteran chairman of the Foreign Relations Committee? Or a president who can’t stop tweet-threatening “Little Rocket Man”? And what about Corker’s claim that the White House is a daily battleground to keep the incumbent under control? Are you going to call one of your own a liar? Or is he right about Trump?

They won’t answer. Knowing how not to answer comes as second nature. More smoothly than Rex Tillerson, they will decline to get into the “silly stuff.” But they should be put on the spot and made to take a stand. Especially the ones who will either face the voters soon—or who are deciding, as Corker did recently, whether that’s even worth it.

(To be clear: every reporter already knows these are the questions to ask, and overall the resilience of the press is one of the heartening aspects of this disheartening era. I’m just spelling out what to look for as day breaks and senators get within reporters’ range.)

For congressional Republicans, this is your moment in history’s eye. One of your colleagues, who has chosen not to run for office again, and who also was the object of one of Trump’s intemperate attacks this morning, has decided that he might as well tell the truth. It turns out that this is often the right way to go! As the (slightly altered) line from Mark Twain put it, by telling the truth you will gratify some people and astonish the rest. Perhaps Corker’s motivations are not the purest or most glorious. He was nice to Trump last year, when Corker was in the mentioning-cloud as a possible secretary of state, and he was part of the “respectable” Republicans who disastrous enabled Trump. Corker’s retorts today followed personal attacks from Trump. Still, he’s doing more than his colleagues have. And Corker has moved toward a better place for himself in the annals of Senate history than he would have had only 24 hours ago.

This most definitely should not be the last step for Corker. If he believes what he says, then as the chairman of the relevant committee in the Senate he has important tools to use. He can issue subpoenas and summon executive branch witnesses as soon as he can get his colleagues back in town. He can draft legislation about the procedure, the grounds, and the justifications before the U.S. commits troops to war. He could urge his colleagues toward the next step through their stages-of-tragedy relationship with Trump. Stage one was carping and dismissal during the first half of 2016, when he was an entertaining long-shot. Stage two was Vichy-regime acquiescence to him during the campaign. Stage three was “support” early this year, toward the goal of the Gorsuch confirmation and the hope of a tax-cut bill. Now we see the inklings of stage four, with the dawning awareness of what Corker spelled out: that they have empowered something genuinely dangerous. It’s time for Corker to act on that knowledge, and his colleagues too.

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As it happens, there’s a convenient precedent for Corker to apply. Just over 50 years ago, his predecessor as chairman of the Foreign Relations Committee was another man from the middle south: J. William Fulbright, of Arkansas. As Ken Burns and Lynn Novick portray in their riveting new documentary series on the Vietnam war, in 1966 Fulbright decided to use his power as committee chairman to convene a high-level, merciless series of hearings on whether his fellow Democrat in the White House, Lyndon Johnson, was making a disastrous error with his deepening commitment to Vietnam. The Senate’s history of the episode recounts:

Attempting to forestall a buildup of American forces, Fulbright launched a high-profile series of widely televised public "educational" hearings in February 1966. [The] testimony prompted an angry President Johnson to order FBI director J. Edgar Hoover to investigate whether Fulbright was "either a communist agent or a dupe of the communists.” Conducted in the Senate Caucus Room, the hearings reached their most dramatic phase when Secretary [of State, Dean] Rusk and General Maxwell Taylor arrived to lay out the administration's case. Fulbright shifted from his earlier role as a benign questioner of supportive witnesses to a grim prosecutor, his dark glasses set resolutely against the glare of television lights. The February hearings did not immediately erode Senate support for Johnson's war policies. They did, however, begin a significant shift in public opinion.

J. William Fulbright had his share of failings, notably alignment with the Old South segregationist forces in the Senate. He was part of the filibuster against Lyndon Johnson’s Civil Rights Act of 1964. Fulbright looks much worse in history’s eyes for that benighted position, while Johnson’s proudest achievements were passage of that bill and then the Voting Rights Act the following year.

But Fulbright was on the right side of history in doing everything he could to change a course of disastrous error set by his own party’s president. He is rightly honored for his foresight, toughness, and courage in taking that stand. And he had at his disposal exactly the tools that Bob Corker will have through the 15 months left in his term: chairmanship of one of the Senate’s most important committees.

Chairman Corker, you’ve seen pictures of Chairman Fulbright countless times in the Capitol and Foreign Relations Committee rooms. You know how he is remembered for what he did 50 years ago. He didn’t manage to avert that era’s war. Maybe you can be remembered for doing better to head off this era’s catastrophe.