You never remind a Jew they converted. It would be like introducing you, “this is Albion Wilde who stole a pack of gum from a 7-11 when he was five years old.”
Stating a fact is not the same as making a negative attack or even a negative assumption. I understand what you are fearing — that someone might try to use the fact of conversion as a negative — but that’s not what’s going on here; just the opposite. The fact that Trump has both Jewish and Christian relatives is a positive asset in his ability to uphold Mosaic-law-based Constitutional norms. He has a personal stake in respecting Jews and the Jewish people, both in Israel as our ally and of course within our nation.