I think a lot of Jews (and particularly Israelis) just can't believe that it's possible for someone to advance a pro-Israel agenda and an anti-Semitic agenda at the same time.
"Look, Trump and his conservative Christian supporters have officially recognized Jerusalem as the capital of the state of Israel, which is what we've wanted America to do for decades now! Look, he's aggressively going after people who have expressed support for the BDS (
Boycott, Divest, and Sanctions) movement! Look, he has a Jewish son-in-law! How could Trump possibly be advancing an anti-Semitic agenda?"
They don't understand that many nominally "pro-Israel" Christians actually think that the Biblical phrase "the people of Israel" applies mostly to
themselves. Christians tend to see
themselves rising from the dead in Ezekiel's "dry bones" vision, and
themselves in the jubilant crowds in the New Jerusalem of the last book of the Christian Bible. They see
themselves in Jacob--later renamed Israel--who managed to transfer both the birthright and blessing of Abraham and Isaac from his unworthy elder brother to himself. They feel entitled to all of the benefits of God's Biblical covenants, with few of the responsibilities. (Sts. Paul and Peter managed to get Christians off the hook for those unpleasant circumcision and dietary requirements, and even the Ten Commandments seem a lot more negotiable when you can just confess and be totally forgiven. Which is why so many conservative Christian politicians in America who cloak their homophobic policies in the mantle of "defense of marriage" have been so demonstrably bad at honoring their own marriage vows.)
The confusion of some Jews about simultaneously pro-Israel and anti-Semitic American politicians is similar to the confusion of American Christians about whether it's possible for someone to support "family values" and "the family as the basic unit of society" while simultaneously breaking up immigrant families and warehousing children in pens, like so much livestock.
"Look, Trump has given us anti-abortion federal justices! He has defended our [perceived] right as employers to deny our employees contraceptives, and our [perceived] right to deny services to same-sex couples, and he even champions our [perceived] right to have random strangers wish us a Merry Christmas instead of non-specific Happy Holidays! We admit that he's not a paragon of Christian virtue himself, but surely God is using him to promote Christianity. So who are we to stand in Trump's way, if he is the instrument of God's holy will?"