There seems to be several Jewish publications that have pointed out that Mandel is Jewish. https://archive.md/wip/SqaQZ

They mostly seem to be upset that he supports Trump and has issued anti-immigrant positions.

Of course being a politician who runs around in Churches carrying a bible, who knows what he really believes and would do once he was in office. It is clear that he is out to deceive people.

The Jew is immunized against all dangers; one may call him a scoundrel, parasite, swindler, profiteer, it all runs of him like water off a raincoat. But call him a jew and you will be astonished at how he recoils, how injured he is, how he suddenly shrinks back: 'I've been found out.'" -Joseph Goebbels