Once again you're overplaying this divide.
Schumer is about as hardcore an Israel backer as they come, like nearly every other "reform" Jew, Bernie included (though he will gatekeep). The notion that reform Jews are less zionist than the Trump Jews is preposterous. Biden's main Jewish powerbroker was Blinken, and he gave Israel a blank check for its Gaza genocide.
Schumer's not completely on board with Mamdani, neither is the largely Democrat, "reform" Jewish NY establishment, other than Nadler. Almost all of them will support Adams, the shabbos goy black Democrat former mayor who has switched parties to become the Republican candidate.