Newsom hits the road to campaign for Biden in Idaho, building his own base in red states
latimes.com
Newsom has made it clear that he wants to be President. The rumor is that he spends the next 4 years planning his run in 2028. Does a Democrat from California have a chance to receive the nomination?
A theory: Biden and the DNC do not want to risk a primary process that could result in the nominee being Sanders or AOC, which could happen if Biden announced he was not going to run for reelection. So, he is officially running for reelection (still/ for now) and thus suppressing an open primary. However, if he were to step back from running late, Newsom's actions like this one would position him as a consensus nominee.
A hiccup in this theory is that usually, Harris as VP would be POTUS's successor (and she would be automatically, if anything happened after the convention). Harris could be positioned better as a next CA governor or maybe even VP again. However, the scope of her popularity is not all that high. Newsom and she could make a deal of some sort.