President Donald Trump and Vice-President Mike Pence with Defence Secretary Jim Mattis, centre, greet military personnel during their visit to the Pentagon last month. Credit:AP Administration officials, including Defence Secretary Jim Mattis and Secretary of State Rex Tillerson, have sought to ease the tension, while at the time same time warning North Korea that if it carried out an attack, it would be met with a crushing response. But they have also underscored that it is Trump's prerogative to use whatever rhetoric he believes is appropriate as commander-in-chief. "I was not elected. The American people elected the President," Mattis told reporters travelling with him on Wednesday. "The rhetoric is up to the President." The "fire and fury" controversy has renewed questions among critics about whether Trump has the appropriate temperament to control the US nuclear arsenal. It also follows a Defence Intelligence Agency assessment, first reported on Tuesday, that North Korea had successfully produced a miniaturised nuclear warhead that could fit inside its missiles.

A US Air Force B-1B Lancer arrives at Andersen Air Force Base in Guam. Credit:Tech. Sgt. Richard P. Ebensberget During his campaign, Trump promised that he would "do everything in my power never to be in a position where we will have to use nuclear power". But he also repeatedly declined to say whether he would use nuclear weapons first in a conflict. On Thursday, he said he would like to "de-nuke the world", but that, until other countries got rid of their nuclear weapons, "we will be the most powerful nuclear nation in the world, by far". A December 2016 assessment by the Congressional Research Service stated that a US president "does not need the concurrence of either his military advisors or the US Congress to order the launch of nuclear weapons".

Additionally, the assessment said, "Neither the military nor Congress can overrule these orders." The reason is simple. The system is set up for the US to launch an attack within minutes, so that if the US is under a nuclear attack, it can respond almost instantly, Bruce Blair, a former nuclear watch officer, said. Before launching a pre-emptive attack, Trump would presumably meet Mattis, his Chief of Staff John Kelly, the Chairman of the Joint Chiefs General Joseph Dunford and the White House National Security Adviser Lieutenant-General H.R. McMaster. However, it would "really be uncharted territory" if they sought to stall or slow down an order from the President, Blair said. Under the existing War Powers Act of 1973, a president is also not required to seek congressional approval for any military action until 60 days after the start of a war.

With new legislation in January, lawmakers Ted Liu, a Democrat from California, and Senator Edward Markey, a Democrat from Massachusetts, sought to stop the President from launching a first-strike nuclear attack until Congress declares war, but the effort hasn't gone anywhere and is unlikely to do so with Republicans controlling both chambers of Congress. Jeffrey Lewis, an expert on nuclear matters at the Middlebury Institute of International Studies, said that he had mixed feelings about the legislation proposed, but "it would be better than what we have now". Trump, he said, is a "walking, one-man campaign for ending nuclear deterrence", the long-held US policy in which it maintains a robust nuclear arsenal in order to prevent other countries from launching a nuclear attack. But Lewis argued it would also be irresponsible to give any president control of nuclear weapons, but then create a system under which those weapons could not be used. It would be better to maintain a small number of nuclear weapons to be used only if the US was attacked, Lewis said.

Steven Hayward, a conservative policy scholar, said that, if Trump's senior military advisers stood united against carrying out a pre-emptive nuclear strike, the "real remedy would be resignation". Hypothetically, doing so might trigger impeachment proceedings, Hayward said, but it isn't clear whether it would be quick enough to stop the President from launching an attack. "It could happen," Hayward said. "It would be pretty dramatic and it would be very unclear what would happen, but it could happen. We're really in uncharted waters here." Bruce Ackerman, a professor of law and political science at Yale University, said that the principle of civilian control of the military also loomed large - "even when the civilian in control is as unpredictable and belligerent as President Trump". Latin American nations have modelled their constitutions along US lines, and their experiences suggest that terrible consequences follow when generals defy their presidents, even under compelling circumstances.

"Worse yet, once the principle is violated, it becomes a precedent for future generals to take the law into their own hands," Ackerman said. Loading "We cannot allow this dynamic to take hold here. If Trump's team can't convince him, they should obey the orders of their commander-in-chief." The Washington Post