Who’s next? The answer, by statute, is the president pro tempore of the Senate. That office would not be vacant. Only 35 Senate seats are up for election in November; the other 65 Senators are now serving terms that extend beyond 2021. So even without an election, there would still be a Senate, though it would have only 65 members.
The next critical question, of course, is who that president pro tempore would be. By Senate practice stretching back to the 19th century, the most senior member of the majority party is selected as president pro tem. Today, it’s Iowa’s Chuck Grassley. If there is no election this fall, however, Grassley would no longer be in the majority party. Of the 65 Senators whose terms continue past 2021, and who would therefore compose the Senate after January 3 in the absence of a new election, 35 are Democrats.
So, by default, the Democrats would control the Senate. To be clear, exactly 18 Democrats could control the Senate, since they’d make up a voting majority of the caucus.
By the usual rules—most senior member of the majority party—the president pro tem, and thus the president of the United States, would be Vermont’s Pat Leahy.
But the pro tem process isn’t a law. It’s just a tradition. And in a world this bizarre, where there’s no election, no president and no House, there’s no reason to assume the Senate Democrats would follow tradition. Legally, they can pick whomever they like. And if what they are really picking is the president of the United States, rather than a ceremonial officer, they might want to exercise some actual choice. They could elect President Amy Klobuchar or President Elizabeth Warren.
But would they? Neither the Constitution nor any statute restricts the choice of president pro tem to a current member of the Senate. (Similarly, the House of Representatives can decide to elect a speaker who is not a member of the House.) So the Senate Democrats could choose anyone at all with the constitutional qualifications to be president—that is, any natural-born U.S. citizen over the age of 35 other than Barack Obama, George W. Bush or Bill Clinton. If they were in a mood to right historic wrongs, they could choose Hillary Clinton. Or for that matter, Al Gore.
The most logical choice, though, would be Joe Biden. He is, after all, the person whom the Democratic Party will have named as its choice for president.