[dredmorbius]

Given Biden's endorsement of Harris, a fellow Californian, Newsom will probably not be on the ticket, due to Constitutional limitations. That's not dispositive, but has generally been interpreted as requiring the two executive candidates to be from different states. The actual language concerns how electors must vote, in Article II, Section I, Clause III:

The electors shall meet in their respective states, and vote by ballot for two persons, of whom one at least shall not be an inhabitant of the same state with themselves.

<https://www.law.cornell.edu/constitution-conan/article-2/sec...>

In strict compliance, this would require California's electors to split their votes on candidates from other states, though other states wouldn't face this limitation.

History.com addressed this earlier this year: "Can the President and Vice President Be From the Same State?" <https://www.history.com/news/can-the-president-and-vice-pres...>

[dredmorbius]

And on reflection: If California's electors couldn't vote for both Harris and Newsom (or any other CA-CA ticket's members), there's the prospect of Democrats winning the Presidential vote whilst Republicans win the VP vote. That would be ... interesting. And all but certainly a prospect that the Democrats would seek to avoid.

So no, a Harris-Newsom ticket is highly unlikely.