Beginning on January 20, President-elect Donald Trump will be accompanied at all times by a military aide carrying the nuclear "football," enabling him to order a nuclear strike at a moment's notice.
Just like his predecessors, whether he is at the White House, in a motorcade, aboard Air Force One or on a trip overseas, he will never be more than an arm's reach away from the aide and his satchel.
"You have to be ready anytime, for any moment," said Pete Metzger, who often carried the nuclear launch suitcase during Ronald Reagan's presidency. "The time is so short between alert and execution."
Less than 15 minutes in the case of an emergency
Trump, like other presidents before him, could have less than 15 minutes in the case of an emergency to get briefed by military aides and make a decision on whether to order a nuclear strike.
"Donald Trump will have the unfettered ability to wage nuclear war," said Joseph Cirincione at The Ploughshares Fund, an anti-nuclear organization.
"He can launch one weapon or a thousand weapons, and no one can stop him, outside of mutiny by the armed forces."
Contrary to popular mythology, the "nuclear football" does not contain a button but instead the equipment and the decision-making papers that Trump would use to authenticate his orders and launch a strike.
The Presidential Emergency Satchel, as it is formally called, contains four things, according to former White House Military Office Director Bill Gulley's book "Breaking Cover."
There is a black book listing a menu of strike options; a 3-by-5-inch card with authentication codes for the president to confirm his identity; a list of secure bunkers where the president can be sheltered; and instructions for using the Emergency Broadcast System.
On Inauguration Day, the aide with the satchel will arrive at the swearing-in accompanying President Barack Obama, and after the ceremony, will accompany Trump.
Trusting Trump with nuclear codes
Not everyone is comfortable with the prospect.
"How can you trust him with the nuclear codes?" Obama said at a rally in Durham, North Carolina, earlier this month. "You can't do it."
And Bruce Blair, a former nuclear missile launch officer who supported Hillary Clinton, says his concerns about Trump persist.
"He has proved himself over and over again to be quick-tempered, defensive, prone to lash out," he wrote in Politico. If a nuclear crisis arises, "Trump's erratic and volatile personality makes for low confidence in his ability to reach the right decision."
A president's order could only be stopped by mutiny, according to Kingston Reif at the Arms Control Association, and only if more than one person were to disobey the president's orders.
"The president has supreme authority to decide whether to use America's nuclear weapons, period," he said. "Full stop."
Trump's transition team did not respond to an inquiry to clarify his nuclear policy. But his rhetoric on the campaign trail may have fed the concerns of his national security critics.
"Somebody hits us within ISIS, you wouldn't fight back with a nuke?" he said to Chris Matthews on MSNBC in March.
But he was more tempered during an interview on NBC's "Today" show in April.
"I will be the last to use it. I will not be a happy trigger, like some people might be," he said.
Still, Trump's disdain for the agreement with Iran to limit their nuclear program has worried proliferation experts, as has his stated openness to allies like Japan obtaining nuclear weapons of their own if they refuse to contribute more to American military protection.
"Wouldn't you rather in a certain sense have Japan have nuclear weapons when North Korea has nuclear weapons?" he said to CNN in March.
A few days later, he walked that back -- but only partially.
"I would rather have them not armed," he said at a rally in Wisconsin. "But I'm not going to continue to lose this tremendous amount of money. And frankly, the case could be made that, let them protect themselves against North Korea."