"And the decision to use nuclear weapons is the most consequential of all".
"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 U.S. national security interests", Murphy explained. "Let's just recognize the exceptional nature of this moment".
"If we were to change the decision-making process because of a distrust of this president, that would be an unfortunate decision for the next president", said Brian McKeon, who served as acting undersecretary for policy at the Defense Department during the Obama administration.
Retired General Robert Kehler said the United States armed forces are obligated to follow legal orders, not illegal ones. Military officers are duty-bound to execute the order. "That is true of nuclear orders as well..."
Kehler responded "Yes, if there is an illegal order presented to military, the military is obligated to refuse to follow it".
"Yes, " Kehler responded, adding such a situation would lead to a "very hard conversation".
Under certain circumstances, he explained: "I would have said, 'I'm not ready to proceed'". Ron Johnson, Wisconsin Republican.
Mr Kehler admitted: "I don't know".
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Stephen Schwartz, a nuclear weapons policy expert and the editor of "Atomic Audit", which assesses the costs of the US nuclear weapons program, said in an interview that the nation is closer than it ever has been in the post-Cold War era to a miscalculation that could lead to nuclear war. "It boggles the rational mind", said Markey, who has sponsored legislation that would prevent any president from launching a first strike. Ed Markey, a Democrat from MA.
He quickly followed that up by saying "I fear that in the age of Trump, the cooler heads and strategic doctrine that we once relied upon as our last best hope against the unthinkable seem less reassuring than ever".
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. "Unfortunately, I can not make that assurance today". Trump wrote on Twitter while on a trip to Asia, using admittedly toned-down rhetoric compared to past statements.
Some of the witnesses agreed.
On the issue of the President being able to start a nuclear war, he was very direct; "Even in the absence of a nuclear attack against our country, no one can tell the president 'no.' Not Secretaries Mattis, or Tillerson".
"He would require lots of people cooperating with him to make the strike happen", McKeon said.
Just a few days after Trump's inauguration, Markey and Rep. Ted Lieu introduced a bill to prohibit the president from launching a nuclear first strike without a declaration of war from Congress. When the president initiates the idea of using a nuclear weapon, particularly in a case of preventive war, there is a coterie of lawyers and advisors in the White House and Pentagon who openly debate the issue.
On Tuesday, former officials cautioned that adding Congress to the equation would hamper the United States response in a high-stress scenario without a lot of time.
For the first time in more than 40 years Tuesday, federal lawmakers on Capitol Hill held a hearing to question the sole authority of a United States president to order a nuclear strike. Gerald Ford was president.