"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 weapons strike that is wildly out of step with USA national security interests".
"Let's just recognise the exceptional nature of this moment". The system requires the president to work with military aides and give orders that must be followed down a chain of command.
But Democrats on the committee were happy to invoke Mr Trump, and they noted that the President's escalating rhetorical battle with North Korea - a nuclear-armed nation he and his advisers have repeatedly threatened to annihilate - lent urgency to their questions about how, if at all, presidents are limited in their abilities to fire nuclear missiles.
For the first time in 40 years, a Senate committee reviewed the president's singular authority to launch nuclear weapons - a move which comes amid increased tensions with North Korea.
Corker has broken publicly with Trump, warning last month that the president was setting the nation "on the path to World War III" with his statements about North Korea and verbal jousting with Kim.
Kim, no stranger to verbal jousting, branded Trump a "dotard". And days after calling on Kim to enter peaceful negotiations, he spoke before South Korea's parliament and listed a litany of alleged human rights abuses against the North Korean leader, calling him a "deranged tyrant" presiding over a "cult".
But "because even a single nuclear detonation would be so consequential and might trigger an escalatory spiral that would lead to civilization-threatening outcomes, we must also have a high assurance that there would never be an accidental or unauthorized use of nuclear weapons", Feaver added.
WASHINGTON ― The only people standing between an impulsive and angry President Donald Trump and thermonuclear war would be high-ranking military officers willing to declare a first-strike order "illegal".
Military experts testifying before the committee noted that, while presidents have ultimate authority to order nuclear strikes, there are safeguards in place to ensure those orders are considered first.
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"I think if we were to change the decision-making process in some way to - because of a distrust of this president, I think that would be an unfortunate precedent", testified Brian McKeon, a former undersecretary of defense under Barack Obama.
The 3 experts agreed there was no strict definition of "imminent", suggesting that a missile on a North Korean launchpad might qualify but that other scenarios might be less clear.
"This continues a series of hearings to examine these issues and will be the first time since 1976 that this committee or our House counterparts have looked specifically at the authority and process for using US nuclear weapons", Corker, who is from Tennessee, said in his statement.
Robert Kehler, an ex-commander of US Strategic Command, said that in his former role he would have followed the president's order to carry out the strike - if it were legal.
But they acknowledged that the President could overrule the advice of his advisers and order a nuclear strike if it is deemed lawful.
Mr Kehler admitted: "I don't know". "But you'd have a real constitutional crisis on your hands if that occurred", he said.
The discomfort among some Republican senators was visible.
"Our adversaries are watching", he said.
"One of the things that voters think about" in U.S. presidential elections, Rubio said, "is whether or not they want to trust him with this capability".