Jeremy Slevin was sitting across from me, and he looked a little uncomfortable. He leaned forward with his hands clasped together. “It’s a really strange, out-of-body feeling to be sitting here as a Jew and be constantly fielding questions, attacks, and accusations of antisemitism,” he told me. Slevin, you see, is a senior adviser to Rep. Ilhan Omar. He oversees her communications. The Minnesota Democrat has faced persistent scrutiny for her comments on Israel, 9/11, and more, which Republicans have sought to keep in the news and used to expel her from the House’s Foreign Affairs Committee last month. But...