During Tuesday’s hearing, the Senate Foreign Relations Committee examined President Donald Trump’s authority to launch a nuclear strike amid rising tensions with North Korea.
"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 strike that is widely out of step with US national security interests," Democratic Senator Chris Murphy said during the hearing.
The committee's chairman, Senator Bob Corker, a Republican, warned that "once that order is given and verified, there is no way to revoke it."
When asked if he would obey an executive order to launch a pre-emptive nuclear strike, retired Air Force General C. Robert Kehler said he would say he is not ready to proceed.
“It would be a very interesting constitutional situation, I believe. The military is obligated to follow legal orders but is not obligated to follow illegal orders,” added Kehler, who led the US Strategic Command under President Barack Obama.
"This is a system controlled by human beings. Nothing happens automatically," he noted.
The Senate hearings come on the heels of mounting tensions on the Korean peninsula following ballistic missile launches and a nuclear test by Pyongyang as well as Washington’s threats to resolve the crisis by force if necessary.
US President Donald Trump has threatened a "devastating" military option and to "totally destroy" North Korea, while North Korean leader Kim Jong-un has warned Washington of "hardline countermeasures" against possible aggression.
In July, the commander of the US Pacific Fleet said that he would launch a nuclear strike on China if President Donald Trump ordered it.
"The answer would be: Yes," Adm. Scott Swift said, responding to a hypothetical question at a security conference at the Australian National University, according to ABC News.
"Every member of the US military has sworn an oath to defend the constitution of the United States against all enemies foreign and domestic and to obey the officers and the president of the United States as commander and chief appointed over us," Swift warned.