He’s a vile man. William F. Buckley actually wrote the definitive work about Buchanan’s anti-Semitism. He compares Buchanan and Joe Sobran, and concludes that Sobran is psychologically obsessed with Jews, and also hates Israel, but is not technically an anti-Semite, but Buchanan is.
I read Buckley's essay, and as best I can recall it concluded BJP was guilty of nothing more than insensitivity.
Sobran's case, Buckley apparently concluded, was different and Buckley kicked him off the NR staff.