Could be an in-party dem power struggle.
Cuomo, discussed as a future pres candidate, would step on Harris (Obama) faction toes. Harris not likable, so competition has to be erased stating now.
Same for Newsom.
OTOH, a Trump boys mission because of SDNY fuckery/impeachment/Article 14 bullshit is possible, too. Timing supports this, IMO. Other dems, like this guy and DeBlasio, see the power vacuum deflating around Cuomo and are walking over his body to get to a better position in the party. Explains Cuomo's reaction. Guy took a shot, but Cuomo ain't dead yet. Will get ugly now.