Donald Trump is claiming, for the moment, that he is on exceptionally good terms with congressional Republicans—even with some of the Republicans that his once-and-future chief strategist Steve Bannon has targeted for political extinction. Indeed, the president declared in his shambolic attempt at a press conference Monday, “maybe, with the exception of a few—and that is a very small few—I have a fantastic relationship with the people in the Senate, and with the people in Congress.”

This is a demonstrably untrue statement. Most Republicans in Congress did not back Trump when he was bidding for the party’s nomination in 2015 and early 2016. Many steered clear of him even after he was confirmed as the party’s candidate. And now a rotating cast of characters in the Senate Republican Caucus continues to trip up what passes for a Trump agenda.

Trump’s relationship with Senate Republicans is not just chaotic. It’s dysfunctional. That produces plenty of fodder for commentary, but not much else. And that’s the problem. Trump is a child-man president who blames everyone else for his foibles. But those who criticize Trump are, for the most part, equally immature. They make grand pronouncements, and garner a good deal of media coverage for it. But they do not take tangible, let alone meaningful, steps to hold this president to account.

Sure, a John McCain may jab at the president’s “spurious nationalism,” as the Arizona Republican did with his Liberty Medal speech on Monday. And a Susan Collins may suggest that she is staying in the Senate to check and balance Trump, as the Maine Republican did last week. Some of these dissenting members may even vote against a Trump-backed proposal, as both McCain and Collins have on the vital issue of health care.

But Trump’s Republican critics—and, to be frank, a number of his Democratic detractors—are not putting the brakes on this presidency.

The decision by Senator Foreign Relations Committee chairman Bob Corker to acknowledge the fact that Trump poses a clear and present danger to the United States and the world offers an example of how the president’s critics fail themselves and their country.

Corker’s objection of Trump is more than just a political story. While television talking heads obsess about the fallout in the Senate—and the impact that the Tennessee Republican’s sudden frankness will have on the 2018 election—Americans have every reason to be unsettled by the prospect that Trump’s threatening tweets and bombastic pronouncements could put the United States “on the path to World War III.”

Corker, a conservative Republican with a hawkish record and a history of enabling rather than challenging this president, is telling them that it is appropriate to fret. “He concerns me,” the senior Republican says of Trump. “He would have to concern anyone who cares about our nation.”

While he was slow to speak up, recent developments explain why even those who were once Trump apologists are starting to worry. When the president addressed the United Nations last month, he squandered an opportunity to calm fears about his instability by telling the chamber that the United States would, if provoked, obliterate a country of 25 million people.

“The United States has great strength and patience,” Trump said during his first address to the General Assembly. “But if it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea.”

Key phrase: “totally destroy.”

So let’s accept that Corker is correct in his concern. But being correct is not enough. The senator needs to do more than simply issue warnings about a president who is in need of “adult day care.” He has a duty to join the members of Congress who are seeking to place limits on Trump’s ability to steer the world toward a planet-obliterating World War III.

Earlier this year, Congressman Ted Lieu (D-CA) and Senator Ed Markey (D-MA) introduced House and Senate versions of their “Restricting First Use of Nuclear Weapons Act of 2017.”

“It is a frightening reality that the U.S. now has a Commander-in-Chief who has demonstrated ignorance of the nuclear triad, stated his desire to be ‘unpredictable’ with nuclear weapons, and as President-elect was making sweeping statements about U.S. nuclear policy over Twitter, observed Lieu, who has emerged as one of the most serious advocates for congressional action to restrain Trump.

Congress must act to preserve global stability by restricting the circumstances under which the U.S. would be the first nation to use a nuclear weapon. Our Founders created a system of checks and balances, and it is essential for that standard to be applied to the potentially civilization-ending threat of nuclear war.

“As long as President Trump has a Twitter account, we need a no-nuclear-first-use policy,” asserted Markey, who recently decried the president’s “escalating, reckless and downright scary rhetoric” regarding North Korea.

The point that these legislators are making is an essential one. Every president has the authority to defend the United States. But, as Markey says,

No president should have the power to launch a nuclear first strike without congressional approval. Such a strike would be immoral, disproportionate and would expose the U.S. to the threat of devastating nuclear retaliation that could endanger the survival of the American people and human civilization.

After Trump’s recent Twitter storms and his stormy speech to the United Nations, the need for Congress to intervene grows more urgent. The Constitution rests the power to declare war with Congress. That power needs to be reasserted and clearly defined as regards nuclear brinkmanship. Leaving Trump leeway to launch a unilateral first strike should be recognized as what Markey says it is: “unconstitutional, undemocratic and simply unbelievable.”

Simply unbelievable, yes, but not necessarily unimaginable with a president so erratic as Donald Trump. Congress must make it clear to the president that he cannot act alone, based on his whims, furies, and fantasies. This should not be a partisan issue. There should be no ideological divide on this one. The stakes are now too high for politics to get in the way.

By signing on as a cosponsor of Markey’s Senate bill, and by using his authority as Senate Foreign Relations Committee chairman to promote consideration of that measure, the senator from Tennessee can take the essential next step. Instead of merely warning about impending danger, Senator Corker should act to avert that dander by joining in legislative efforts to check and balance Donald Trump.