He and his party are doing the calculus and figuring that they'll do better supporting Israel because, frankly, where else are those voters going to go? Trump? He'd nuke Gaza if Netanyahu co-signed a loan for him.
Democratic voters need to vote blue no matter who, and then primary out the corporatist candidates at the earliest opportunity.
This has to be a two-pronged effort: keep the Republicans out of office permanently, and clean the Democratic slate from within.