Being "pro-Israel" doesn't necessarily preclude antisemitism. Lots of weird mental gymnastics going on with some folks.

E.g. Trump who according to himself is a bigger friend of Israel than Jews living in America are, while at the same time using the Star of David to label political opponents as corrupt, feeding antisemitic cliches by claiming various media is controlled by Jews, suggesting American Jews are disloyal because they serve Israel first, ...

Majorie Taylor Greene also finds time to blame anti-Israel positions for violence against Jews - inbetween her bullshit about Jews running everything and plotting evil things.

Then there's the entire thing with the Evangelical Zionists, where the origin is the belief they need to support Israel for theological reasons - but not necessarily to support Jewish people (especially not those outside Israel), but as a tool.

To a degree probably also geopolitics: it makes sense to support Israel if you hate their opponents (Arab Muslims) even more.