What happens with Power transition (Inauguration) during Emergency

Question

Suppose Biden is undergoing the Presidential Inauguration and some emergency event (Fire alarm, alert to potential disruptive crowds/hostiles) makes the President incapable of performing the formalities and complete his oath, who would be the de-facto president then?

At Noon, the Previous President(Trump) would already be out of his office and Biden is not exactly "Incapacitated" which would have allowed for Section 3 of the 20th Amendment:

"Section 3. If, at the time fixed for the beginning of the term of the President, the President elect shall have died, the Vice President elect shall become President.

Which would yield VP to gain power. But Biden won't be 'dead', merely incapicated. This seems confusing - Trump would officially have resigned but Biden wouldn't have been officially been made President. Would Kamala Harris be then the Temporary President?

What happens in this case? Who would hold the power? What are the legal provisions to prevent misuse of power by the Previous President (Trump) during this time, or his aides?

Edit: There was a simple misunderstanding - I meant that the emergency happened before the Inaugaration posing problems regarding the formalities involved and deciding who would the President in power.

Answer 1

Details influence the exact outcome, but these pieces of information are relevant:

1. The public ceremony is not required for the president elect to become the president. If January 20 falls on a Sunday, the president will be sworn in that day by taking the oath privately, but will then re-take the oath in a public ceremony the next day, on January 21.

2. At noon, not only is the President no longer president, the VP is also no longer VP. The Presidential Succession Act spells out who's next in line, which would be the Speaker of the House, if available.

3. There are three nuclear footballs in total. Two are allocated to the president and vice president, with the last being stored in the White House.[14] In Presidential transitions, the president-elect does not receive the actual nuclear code card until after the nuclear briefing, when "he meets with the outgoing president at the White House just before the actual inauguration ceremony. The code card is activated electronically right after the president-elect takes the oath at noon".[15] -Wikipedia

4. "Power resides where men believe it resides." During an actual emergency, courts are far too slow, and complex rules are subject to subjective interpretation. Ad hoc improvisation will determine who's in charge, with "President elect", "(former) President", "VP", and "nobody" all being on the table. There are multiple people involved in the execution of orders, and they are humans who operate on personal beliefs, not computers who operate on code.

Answer 2

The oath of office doesn't take long to administrate and can be done quickly if needed the entire public ceremony is what takes time. If there was some sort of issue that would cause problems doing as expected they would likely do it as they moved him to a safer location.

Answer 3

The President is the President, ie Biden. His term of office begins at noon, oath or no oath. No "inauguration" is required. Trumps term ends and instantly Biden's term begins. (Pratchett would say it happens faster than the speed of light)

I think you are misunderstanding the intension of "incapacitated". That means (for example) undergoing a general anaesthetic, or too sick to make any kind of decision. It is not about oaths.

In case that there is significant disruption to the ceremony, the President goes inside, where (it is assumed) he is safe. He probably takes the oath there and then. The Constitution doesn't say that the chief justice has to administer the oath. We know that any Federal Judge can do so (Sarah Hughes) is is likely that any judge, commissioner or clerk of a court of record having a seal, master in chancery, notary public authorized to administer oaths can legally administer the oath.

There may then be a delayed ceremony when safe to do so. One is permitted to retake the oath as many times as desired.

No provisions are specially required. Trump would no longer be President.

Answer 4

As other answers mentioned, the President could take the oath privately, in any place, if events prevent the public ceremony from taking place, so there is no reason why the President would remain in a state of not having taken the oath for long unless he was actually in a coma or something.

If, hypothetically, the new President decided to play some kind of prank and chose to not take the oath indefinitely or something, then I think technically he would still be President, but just not have the powers of the Presidency. Article II, Section 1, Clause 8 of the US Constitution says

Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation: [...]

It doesn't say "before he becomes President", just "before he enter on the execution of his office", which I think means the powers of the Presidency. So in the case where the President choose to not take the oath indefinitely, I think technically nobody would have the powers of the Presidency.

I am not sure whether the VP or people further down in the order of succession can act as President in this case. The Presidency isn't actually vacant, but I guess they could declare that the President is unable to discharge his duties (using the 25th Amendment or otherwise) due to his not having taken the oath, to pass the powers onto someone further down in the order of succession. Alternately, they could try to impeach him.

In any case, both invoking the 25th Amendment and impeachment require a deliberate process and is not something that would happen automatically just because the President hasn't taken the oath, so there is nobody that assumes the powers of the Presidency in the normally short gap of time between noon and when the new President takes the oath.