Donald Trump could launch a nuclear weapon, and no one — not Congress, not the chairman of the Joint Chiefs of Staff, not the secretary of defense — could stop him.

That unchecked presidential authority was called into question Tuesday in a Senate hearing led by Republican Sen. Bob Corker of Tennessee, as tensions over North Korea spurred fears of a knee-jerk reaction from the president.

“Let me pull back the cover, for a minute, from this hearing,” said Sen. Chris Murphy, Democrat of Connecticut. “We are concerned that the president of the United States is so unstable, is so volatile, has a decision-making process that is so quixotic, that he might order a nuclear weapon strike that is wildly out of step with U.S. national security interests.”

“Let’s just recognize the exceptional nature of this moment and the discussion we’re having today,” Murphy added.

Ultimate power

Panelists and senators went back and forth for well over an hour, debating issues ranging from whether a nuclear war should be authorized by Congress to the military’s duty to refuse orders if illegal. Trump’s comments on Pyongyang in the last several months were the impetus for the hearing.

“‘Can the President really order a nuclear attack without any controls?’ That question is asked more and more by the American people. And of course, it’s fueled by comments made by President Trump,” said Democratic Sen. Ben Cardin of Maryland, the ranking member of the Senate Foreign Relations Committee. “Many interpret that to mean that the president is actively considering the use of nuclear weapons in order to deal with the threat of North Korea.”

“That is frightening,” Cardin added.

American presidents wield a tremendous amount of power when it comes to launching nuclear weapons. Unlike when deploying conventional troops, which requires congressional approval, starting a nuclear war is solely in the president’s hands.

The system is designed so if the president of the United States wants to attack another nation with a nuclear weapon, he can do so quickly and without bureaucracy. As Alex Wellerstein, a nuclear historian, plainly wrote in the Washington Post after Trump’s election, “There is no failsafe.”

“The one sure way to keep President Trump from launching a nuclear attack, under the system we’ve had in place since the early Cold War, would have been to elect someone else,” Wellerstein wrote.

One caveat

But retired U.S. Air Force General Robert Kehler, who sat on the panel Tuesday, did caveat the president’s authority with the notion of legality — that the military is obligated to refuse any illegal order.

“If there is an illegal order presented to the military, the military is ordered not to follow it,” said Gen. Kehler. However, the decision of what is illegal “would be a very difficult process and a very difficult conversation.”

Tensions have escalated between Pyongyang and Washington for months now. Trump threatened to “totally destroy” North Korea in his inaugural U.N. speech, on the heels of comments where he warned of “fire and fury.”

“North Korea best not make any more threats to the United States. They will be met with fire and fury like the world has never seen,” Trump said on Aug. 8.