The last time a president refused to show up at his successor’s inauguration — Andrew Johnson in 1869 — the United States did not possess the world’s deadliest nuclear arsenal, and it would be seven decades before Washington first established the principle that the commander in chief would be given sole authority to launch it.
So the handoff of power from President Trump to President-elect Joseph R. Biden Jr. on Wednesday includes a grim new piece of choreography involving the fate of two nuclear footballs and — more important — two sets of nuclear launch codes, contained on a card called “the biscuit.”
Mr. Trump’s codes are to go dead at noon, like a canceled credit card. And Mr. Biden’s go live as soon as he is sworn in.
That, at least, is the theory. It has never been tried before at this distance. In past inaugurals in the nuclear age, the football — and all the authentication procedures and the authorities that go with it — moved imperceptibly from the departing president sitting at the dais to the incoming one standing with the chief justice of the United States.
In this case, one football, and Mr. Trump’s biscuit, will be in Florida. Another set, Mr. Biden’s, will be on the West Front of the Capitol, in the same spot where a violent effort to prevent that transition from happening took place two weeks ago.
“This is entirely unusual,” said Scott Sagan, a Stanford University professor who has written extensively on nuclear command and control. “There is no reason to think it wouldn’t work technically.”
But there was a seamlessness to the process when both the incoming and retiring presidents were on the same stage, one that made it harder for an adversary to exploit the transition of power.
“President Trump’s decision not to attend the inaugural just puts an unneeded complication, and some more risk, into this process,” Mr. Sagan added.
The Pentagon will say nothing about how it is preparing for the moment. And Mr. Biden’s transition team would not talk about it either, referring questions back to the departing administration.
But Mr. Biden would not be new to the process. As vice president, and the one who would inherit nuclear launch authority if the president were incapacitated, he would have been briefed often on the elaborate system of authenticating an order.
In ordinary times, this handoff would hardly raise an eyebrow. But in recent weeks, Democrats pressing for impeachment or the invocation of the 25th Amendment have frequently cited Mr. Trump’s sole authority to launch nuclear weapons to make the case that he should be removed before Jan. 20.
Less than two weeks ago, Speaker Nancy Pelosi called the chairman of the Joint Chiefs of Staff, Gen. Mark A. Milley, in what seemed to be an effort to have the Pentagon leadership offer assurances that Mr. Trump would be removed from the nuclear chain of command. She then made the call public, saying it was important that “an unhinged president” did not have access to nuclear codes.
General Milley made no commitment, and such an act would be illegal unless the cabinet invoked the 25th Amendment or the president was convicted on the impeachment charge that the House approved last week.
All of which put new focus on what may be the most visible element of the transfer of power. And there are questions about whether the Pentagon was even fully cooperating on that and a range of other transition issues.
“We’re living in an era of some unpredictability,” said Seth G. Jones, the director of the international security program at the Center for Strategic and International Studies, a Washington think tank. “In most transitions, there’s a pretty constant state of cooperation between the incoming and outgoing administrations. Here, there’s been a lot of turmoil, particularly with the Department of Defense.”
If a nuclear crisis were to erupt on Inauguration Day, Mr. Jones continued, “it could pose a cooperation issue.”
“One hopes that, in a crisis, adults can cooperate,” he said. “But there’s been a lot of drama, and that’s a cause for some concern.”