(3) He needs to protect Kamala Harris.

As Biden’s vice-president, Harris is his heir apparent. But that doesn’t mean she’s anything like a lock for the 2024 presidential nomination if Biden does decide not to run.

Since World War II, four sitting vice-presidents have run for the big job. The first, Richard Nixon, won the 1960 Republican presidential nomination by near-acclamation, though not without making some controversial policy concessions to keep Nelson Rockefeller from challenging him. Subsequently Hubert Humphrey (in 1968), George H.W. Bush (in 1988), and Al Gore (in 2000) had to win their party’s nomination against serious opposition.

Harris is positioned well ideologically to unify Democrats if she runs as Biden’s preferred successor. But she has some significant popularity issues, and the Beltway insider class that influences media coverage has regularly disrespected her.

The longer Biden freezes potential opposition in place by planning — or pretending to plan — a reelection campaign, the easier it would be for Kamala Harris to take over that campaign and marginalize rivals.