Sen. Chris Murphy (D., Conn.) expressed concern Tuesday that President Donald Trump is "so unstable" and "volatile" that he could order a nuclear strike that is "wildly out of step" with US national security interests.
Retired Air Force Gen. Robert Kehler, who previously served as the commander of US Strategic Command under President Barack Obama, explained that there are layers of safeguards within the current system created to ensure any order is both legal and proportionally appropriate.
"It boggles the mind that there is not at least one Constitutional office holder that has to be consulted before a nuclear strike is ordered", he said. He added that if he was uncertain of the legality, he would consult his own advisers.
Under certain circumstances, he explained: "I would have said, 'I'm not ready to proceed'".
"I don't know", Kehler replied, to nervous laughter in the committee chambers.
People in the room laughed.
No Trump administration officials are testifying before the hearing, which is examining the nuclear command and control structure that has served all USA presidents.
Dr. Peter Feaver, a professor of public policy and political science at Duke University, also highlighted the point that any nuclear launch would be preceded by a review and consultation process.
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Corker publicly questioned Trump's decision-making abilities last month when he expressed concern over the president's heated rhetoric that, in his view, undermined USA diplomatic efforts with foreign adversaries and put the country "on the path to World War III".
When asked before the hearing if he was concerned about Trump's authority, Corker said, "This is not specific to anyone".
Another senator on the panel has drafted legislation proposing to curb the president's power to launch a nuclear attack.
Despite rallying 13 co-sponsors in the Senate, the measure has no Republican support and has gained little traction. Indeed, a military aide shadows the commander in chief day and night, carrying the black briefcase commonly referred to as the "nuclear football", packed with attack options and other information needed in a national emergency.
The president, as commander in chief, is the sole arbiter or whether to use the US nuclear arsenal - an issue that hasn't been debated at the congressional level in more than 40 years.
Under current rules, the U.S. president could set a strike in motion by entering the codes into a device called "the football", which travels everywhere with the president.
The closely watched discussion, led by a prominent Republican Trump critic, addressed a hypothetical presidential decision to launch a nuclear first strike against a USA adversary.
This is because an enemy ballistic missile launched from the other side of the world could hit the United States in barely 30 minutes.