Anyone who was expecting diplomacy or nuance from Donald Trump in his United Nations speech got a jolt Tuesday morning. Trump appeared before the UN General Assembly as a commander in chief rattling his nuclear sabers.

Trump actually repeated aloud his Twitter reference to North Korean dictator Kim Jong Un as “Rocket Man,” telling world leaders in the most important foreign-policy address so far in his presidency that “Rocket Man is on a suicide mission for himself—and for his regime.”

The presidential name-calling shredded any hope for delivering a credible message to the regime that has been taunting its neighbors with missile launches. Trump told the UN, “It is time for North Korea to realize that its denuclearization is its only responsible future.” That was a reasonably well-stated demand. Unfortunately, it will never be so fully noted or fully recalled as the determination of the president of a major nuclear power to employ an Elton John song title for the purpose of poking at the “supreme leader” of a rogue nation that aspires to be a nuclear power.

Nor will the search for a diplomatic solution be advanced by Trump’s griping on Tuesday about the Obama administration’s agreement with Iran to constrain its nuclear program,. “The Iran deal was one of the worst and most one-sided transactions,” he announced. His suggestion that the agreement was a mistake increased speculation that the deal will soon be scrapped, leading France’s foreign minister to warn about the prospect of a “spiral of proliferation.”

Worse yet, Trump 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.”

There will be plenty of reactions from around the world to Trump’s intemperate address. But there should also be a reaction from the US Congress.

Earlier this year, Congressman Ted Lieu, D-California, and Senator Ed Markey, D-Massachusetts, 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. “President Trump’s speech to the United Nations will be remembered not for rallying the international community around our common challenges, but instead for threatening another nation with annihilation,” warned Congressman Lieu on Tuesday. “Let us be clear: the issue is not whether the U.S. is capable of destroying North Korea, but rather whether we are willing to allow South Korea, Japan, and potentially Guam to be destroyed in the process—along with hundreds of thousands of American lives.”