The Constitution establishes a chain for who becomes "acting president" if the president is incapacitated — but even if President Trump and Vice President Mike Pence both fell ill from the coronavirus, many responsibilities could be delegated to White House staff before they'd turn to House Speaker Nancy Pelosi.

Why it matters: It's highly unlikely, but given Trump's positive COVID-19 test, there's a protocol under Section 3 of the 25th Amendment of the Constitution for Trump to temporarily cede authorities to Pence.

• If Pence is incapacitated, the power could pass to the speaker of the House of Representatives, a Democrat and one of the administration's fiercest foes.

Be smart: Pence tested negative for the virus again this morning. And the president himself could feel very sick and still be able to continue doing his job.

What they're saying: "If both the President and Vice President are very sick but functioning, they can delegate decisions to subordinates," said Jonathan Turley, a professor of law at George Washington University.

• "Actual succession under the 25th Amendment only kicks in with an effective vacancy due to death or complete incapacity."
• Section 3 has been invoked three times since its adoption in 1967 — all for short-term medical procedures. Ronald Reagan invoked it once, and George W. Bush did it twice.

How it works: The president could send written notification to the Speaker of the House and Senate's president pro tempore that he is "unable to discharge the powers and duties of his office," thereby making the vice president the acting president.

• When the president decides that he's fit to assume duties again, he would send another "written declaration to the contrary" to the two congressional leaders, and he's automatically president again.
• In July 2007, Vice President Dick Cheney served as acting president for a little more than two hours after Bush wrote this letter, before he underwent a colonoscopy.

Between the lines: Section 4 of the 25th Amendment lays out a process if the vice president and a majority of the cabinet needed to declare that the president is incapacitated.

• While a provocative topic, Section 4 has never been invoked. Were there a dispute between the president and vice president over capacity to serve, it would come down to a two-thirds vote of Congress.