The commander of U.S. nuclear forces says he would resist any "illegal" order from a president to launch a strike and would attempt to recommend an alternative move.
Air Force General John Hyten, the commander of U.S. Strategic Command, told a forum in Halifax, Canada, on November 18 that he had discussed the scenario with President Donald Trump.
He said he would tell Trump or any future president that an order to launch nuclear weapons can be refused if that order is determined to be illegal.
"We think about these things a lot. When you have this responsibility, how do you not think about it?" Hyten said. "I provide advice to the president; he'll tell me what to do."
"If [a command] is illegal, guess what's going to happen? I'm going to say, 'Mr. President, that's illegal.' And guess what he's going to do? He's going to say, 'What would it be legal?' And we'll come up with options, of a mix of capabilities to respond to whatever the situation is, and that's the way it works. It's not that complicated."
The U.S. Strategic Command would control nuclear forces in a war. It also has responsibilities for U.S. cybercapabilities and missile defense.
The issue of the potential use of nuclear weapons has come to the forefront amid the standoff with North Korea over its nuclear and missile programs.
On November 14, U.S. senators began debating the limits of a president's unilateral power to launch a nuclear attack.
Senators and expert witnesses agreed that, in the event of an ongoing or imminent nuclear attack, the president had the constitutional authority to defend the nation.
But some senators expressed concerns that an impulsive president has the power to unilaterally unleash a first-strike nuclear attack.
During the hearings, retired General Robert Kehler, who headed Strategic Command from 2011-13, cited a military precept: "The military is obligated to follow legal orders, but is not obligated to follow illegal orders."
With reporting by AFP and AP