It is a useful confluence of events that President Trump issued a tweet about nuclear weapons that many experts regard as perhaps his most dangerous and crazy tweet yet — at exactly the moment that Mitt Romney is considering a run for the U.S. Senate from Utah.

It is useful, because a Romney run — and victory — could set an example for other congressional Republicans to follow when it comes to acting as a check on Trump’s many excesses, from his dangerous international bluster, to his self-dealing and corruption, to his contempt for norms and the rule of law. If they don’t follow that example, their enabling of these Trump excesses will be thrown into sharper relief.

That is, this might be the case, if Romney is true to his own past statements about Trump. Let’s not let this get memory-holed: In his big March 2016 speech against Trump, Romney flatly and unequivocally declared Trump unfit to serve as president. Will Romney reiterate this sentiment, when he’s running for Senate?

Last night, Trump tweeted that his “Nuclear Button” is “much bigger & more powerful” than the one that Kim Jong Un boasted about. Many experts have denounced this as needlessly belligerent and deeply reckless amid an escalating situation that carries the possibility of unspeakable horror. Some cast it as the latest sign of Trump’s unfitness: Former Bush official Peter Wehner noted that we are “watching an American president psychologically, emotionally and cognitively decompose.”

Meanwhile, we are told that if Romney is elected to the Senate seat of the retiring Orrin Hatch, he will act as a “foil” to Trump. Politico reports that Romney has told big GOP donors that he will speak out against the president. CNN reports that Romney will have “no qualms” about “directly challenging” Trump’s “temperament” and “moral leadership.”

Liberals will scoff at this, and point out that Romney will vote for Trump’s policy agenda 99.9999 percent of the time. This is likely true. But, if you view it as a central fact of this moment that our president’s temperament renders him catastrophically unfit to serve, and that he is degrading our norms and politics and institutions in all kinds of deeply dangerous ways — and that congressional Republicans are enabling all of this, when they could be acting to mitigate the damage — then we should hope that Romney does become at least a serious voice of opposition to Trump.

The Fix’s Amber Phillips explores the potential ramifications of the upcoming retirement of Sen. Orrin G. Hatch (R-Utah.). (Bastien Inzaurralde/The Washington Post)

And hoping for this means holding Romney to what he said in his March 2016 speech. In it, Romney flatly declared that Trump “has neither the temperament nor the judgment to be president.” Trump’s performance in office has resoundingly vindicated Romney’s judgment. When he becomes a politician again, will Romney acknowledge that Trump has vindicated his judgment?

We don’t know. But it would have real value if he did. When Sen. Bob Corker (R-Tenn.) denounced Trump as a global danger who must be constrained by his inner circle, it forced a public debate on Trump’s unfitness and, in the process, revealed just how dangerous the continued Republican enabling of him has become. Romney could do the same.

If we are holding Romney to his own 2016 speech, then there are other things he must be asked. In the speech, Romney also denounced Trump for not releasing his tax returns. Okay, does Romney think the congressional GOP should take steps to bring that about? It’s one thing to denounce Trump’s ugly, hateful rhetoric. But does Romney think Trump’s unfitness is also on display in his contempt for the rule of law? Does Romney think Republicans should more forcefully signal that any effort to remove special counsel Robert S. Mueller III will be unacceptable? Does Romney think Republicans should stop helping Trump’s media allies spin a fictional alternate narrative in which ongoing law enforcement efforts to establish the truth about Russia and 2016, and hold Trump and his top officials accountable for their own actions, are relentlessly painted as corrupt and illegitimate?

Key moments from a speech in which former GOP presidential nominee Mitt Romney said Donald Trump "is playing the members of the American public for suckers" (Sarah Parnass/The Washington Post)

It will be argued that politicians always say things in the heat of primaries for which they perhaps should not be held accountable later. But Romney’s 2016 speech came when he was not a candidate, and it has been widely treated as something different from conventional rhetoric — as a genuine last stand of sorts, a grand statement of principle, a desperate effort to keep the light of true conservatism shining amid the GOP’s surrender to encroaching darkness and possible tyranny. As Ross Douthat puts it, Romney’s stand was “an exemplary act that threw the cowardice of his party’s establishment into sharp relief.”

If we are going to treat that moment in such grandiose terms, Romney should now be judged against it. I don’t think Romney will pass this test. If he does not, this will have a perverse value of its own, illustrating once again that Republicans must jettison their own principles to accommodate themselves to Trump, in ways that they themselves know are dangerous to their country’s future, to get along with GOP voters and make their way within the party. But we should all hope he does pass it.

* TRUMP’S TWEET SEEN AS DANGEROUS AND CRAZY: Last night Trump tweeted that his nuclear button is bigger than Kim Jong Un’s. The New York Times sums up the reaction:

The president’s tone also generated a mix of scorn and alarm among lawmakers, diplomats and national security experts who called it juvenile and frightening for a president handling a foreign policy challenge with world-wrecking consequences. … Many security experts have said there is no reasonable military option for restraining North Korea that would not involve unacceptable loss of life.

Meanwhile, Trump allies, such as Michael Flynn Jr., who just made a plea deal, are bubbling over with excitement, seeing this as a show of Trump’s strength.

* NUKE TWEET MAY BE UNPRECEDENTED: CNN’s Stephen Collinson analyzes the tweet:

Before Trump, no US President has made such public and cavalier threats, apparently relishing the power he wields as the person who could, by himself, deploy America’s earth-shattering nuclear arsenal within a matter of minutes.Trump’s gambit is all the more risky since it is likely to alienate U.S. allies, anger key world powers like Russia and China that Washington needs to resolve the standoff.

But angering international elites shows Trump is winning, right?

* FUSION GPS FOUNDERS SPEAK OUT: Republicans say the “Steele Dossier” started the FBI probe of possible Russia-Trump collusion. But the founders of Fusion GPS, the firm behind the dossier, are now denying the claim and detailing what they told Congress:

Republicans have refused to release full transcripts of our firm’s testimony, even as they selectively leak details to media outlets on the far right. It’s time to share what our company told investigators. We don’t believe the Steele dossier was the trigger for the F.B.I.’s investigation into Russian meddling. As we told the Senate Judiciary Committee in August, our sources said the dossier was taken so seriously because it corroborated reports the bureau had received from other sources, including one inside the Trump camp.

Someone will get his or her hands on this testimony soon enough.

* TRUMP MAY STILL PULL OUT OF IRAN DEAL: Politico reports that the anti-government protests in Iran may cause Trump to pull out of the Iran nuclear deal, in spite of his advisers’ advice to the contrary:

Some people familiar with administration deliberations say that the moment of vulnerability for Iran’s nearly 40-year-old fundamentalist regime may move him to grander action. … [But] middle East experts and former U.S. officials [warn] pulling the plug on the nuclear deal would throw Iran’s embattled Islamist leaders a lifeline. The agreement retains strong support from the five other nations that negotiated it with Tehran — China, Russia, Great Britain, France and Germany.

Needless to say, Trump will only be concerned with how his own actions appear to his dwindling hard core of supporters and not with the international consequences of those actions.

* REPUBLICANS FACE NEW PRESSURE ON OBAMACARE: USA Today reports that some Republicans still want to repeal the Affordable Care Act, but there may be new pressure on GOP leaders to shore up the individual markets:

This time around, Republicans will face more pressure to act, especially in the Senate. That’s because Senate Majority Leader Mitch McConnell, R-Ky., promised a key GOP moderate he would push for passage of two bills designed to stabilize Obamacare and keep premiums down in the individual insurance market. In exchange, Sen. Susan Collins, R-Maine, agreed to vote in favor of the GOP tax bill.

The tax bill includes mandate repeal, which could spike premiums. It remains to be seen whether Republicans will act constructively on health care rather than only doing as much damage as possible.

* TRUMP ADMINISTRATION’S DANGEROUS CHANGE TO CENSUS: The Justice Department wants a question about citizenship status added to the census. The Post has a good editorial explaining the practical dangers of this move. Note this:

Since its inception, the census has not only counted voters; it has taken a precise snapshot of everyone in the country. This helps government agencies to direct scarce dollars … It is also crucial for doling out congressional representation. … Asking about citizenship status would deter undocumented people — or even legal immigrants who fear how far the Trump administration’s crackdown on foreigners will extend — from returning census forms. Many states — particularly blue states — could end up shortchanged.

Maybe this is intended as a feature of the plan, and not a bug?

* AND HERE’S HOW TRUMP’S BIG BUTTON REALLY WORKS: NBC News reminds us that Trump doesn’t actually have a nuclear button. Instead:

The process for launching a nuclear strike is secret and complex and involves the use of a nuclear “football,” which is carried by a rotating group of military officers everywhere the president goes and is equipped with communication tools and a book with prepared war plans. If the president were to order a strike, he would identify himself to military officials at the Pentagon with codes unique to him. Those codes are recorded on a card known as the “biscuit” that is carried by the president at all times. He would then transmit the launch order to the Pentagon and Strategic Command.

Your regular reminder that even before Trump was elected, nuclear experts worried about what might happen if Trump tweeted about nukes, which is exactly what’s happening now.