There are a few others who didn’t have a vice president prior to the 25th Amendment setting up a procedure to fill a Vice Presidential vacancy..
Harry Truman did not have a vice president from April 1945 when he succeeded FDR until he was elected in 1948 with his running mate Alben Barkley.
Teddy Roosevelt didn’t have a vice president from the time he succeeded McKinley in 1901 until the 1904 election when Teddy was elected president in his own right.
Four?
Teddy Roosevelt immediately comes to mind as a fifth.
...and Ford was never elected to Vice President nor President. Squeaky Fromme referred to that as part of her reasoning for attempting to assassinate him.
There’s about four months until the election. If Biden stepped down today, it’s super unlikely that Harris could get a replacement VP confirmed through a divided congress AND run a winning campaign for President. The confirmation hearings would just be a circus, and a very unpredictable one at that.
If, however, you wanted to really hamstring incumbent Republicans from campaigning, it would be a really effective method of freezing them in place.
It’s actually FIVE. You really can’t count Harris as a VP. She’s a DEI hire.
So without a VP, a President has no tiebreaker vote (presumably supporting the President) in the Senate?