News that President Donald Trump tested positive for COVID-19 has thrown a wrench into his presidential campaign, and if he experiences complications, he may have to yield power to Vice President Mike Pence.

Trump tweeted early Friday morning that he and first lady Melania Trump have the coronavirus. Pence and his wife Karen tested negative Friday. Under the 25th Amendment to the Constitution, Pence would assume control of the country if Trump, 74, becomes incapacitated in any way, even on a temporary basis.

According to CNBC, Brookings Institution senior fellow John Hudak published a research note earlier this year that outlined what would happen if Trump turned in a positive test for the virus. He said aside from isolating the president from everyone else, including his security detail (which could keep tabs on him via remote technology), the people in the line of presidential succession would also be isolated.

Pence is first in line to take over the presidency, followed by House Speaker Nancy Pelosi, and Sen. Chuck Grassley, R-Iowa. Grassley is the president pro tempore of the Senate. Behind them are the members of the Cabinet, beginning with Secretary of State Mike Pompeo.

In a worst-case scenario, Trump could be replaced on the November ballot by another presidential candidate, which would be chosen by the Republican National Committee. According to The Daily Mail, the 168 members of the RNC would vote to nominate another candidate, which could be Pence or someone else.

With around 1 million votes already cast for the election and mail-in ballots already going out, however, replacing Trump on the ballot would seriously disrupt the process.