(CNN) - A decades-old presidential authority to use nuclear weapons is suddenly coming into question as US allies and some lawmakers from both parties want the Trump administration to assure them that President Donald Trump cannot rashly launch a nuclear strike, according to multiple sources.
The potential that Trump could use existing law to authorize the deployment of a nuclear weapon on his own is becoming the subject of frequent conversation -- and bipartisan anxiety -- on Capitol Hill. Senate Foreign Relations Committee Chairman Bob Corker will hold a hearing Tuesday on the authority of the President to maintain sole authority to launch nuclear weapons.
It's a big day on Capitol Hill: Follow along live
A NATO partner country raised concerns about the President's command of the US launch system. A diplomatic source from that country said they were more comfortable following a briefing on the subject.
"The more people think about this, the more they realize Donald Trump can start a nuclear war," Sen. Ed Markey, a Massachusetts Democrat who sits on the Foreign Relations panel, said in an interview.
The administration is trying to soothe concerns by arguing the existing launch process that presidents have operated under for decades has sufficient checks in place that would discourage Trump from taking imprudent action. Trump himself has had multiple briefings on the nuclear launch cycle and more conventional, non-nuclear alternatives.
The requests for assurance come as Trump has rattled Washington and other world capitals with heated rhetoric toward North Korean leader Kim Jong Un. Tuesday will mark the first time the Senate Foreign Relations Committee has held a hearing on a president's authority to use nuclear weapons since 1976, according to the panel.
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Corker, who has announced he won't seek re-election next year and has become a frequent Trump critic, has said he would use his committee chairmanship to keep the President in check.
"The committee is going to be very active," he said in October. "I think it will be very informative to the American people and the rest of the Senate about what powers the President has -- should, shouldn't have, whatever. It's going to be a very robust period of time."
The White House did not respond to requests for comment on Corker's decision to hold a hearing on the President's nuclear authority.
The administration's attempts to assuage the growing concerns underscore the fact that, like his predecessors, Trump has sole authority to decide when and how to use nuclear weapons.
If there is a sense that Trump rashly ordered a nuclear launch, multiple sources tell CNN that senior generals would explain the risk of such a move. But that's not specific to Trump -- top military officials would offer advice to any president facing the extraordinary decision of whether to launch a nuclear weapon.
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A central question surrounding the potential of a nuclear launch is whether it would cause undue widespread human suffering when there are other, less dramatic military options. Under US military law, troops are obligated to not obey an unlawful order. If they received such an order, they could resign or force Trump to fire them.
The military continues to argue that with the advent of precision weapons such as cruise missiles and heavy bombers, there is less reason to use nuclear weapons. In developing options for North Korea, the Pentagon has a package of what it calls flexible response options, which includes ensuring US aircraft and missile launching ships are always in place if needed.
There's no secret alternative chain of command in place. The military would treat Trump as they would any other president ordering a nuclear strike. To do otherwise would be considered treasonous.
During an Oct. 30 Senate Foreign Relations committee hearing, Defense Secretary James Mattis said the launch process is "extremely rigorous."
But he resisted calls for changes. Markey is sponsoring legislation that would require a congressional declaration of war before a president could authorize a first-use nuclear strike. During the Oct. 30 hearing, he pressed Mattis on whether he could contemplate a scenario in which Trump authorized a nuclear strike on a country that didn't first launch a nuclear attack on the United States.
"If we saw they were preparing to do so and it was imminent, I could imagine it," Mattis said. "It's not the only tool in the tool kit to try to address something like that. But I believe congressional oversight does not equate to operational control. I think we have to keep trust, keep faith in the system that we have, that's proven effective now for decades."