Elon Musk, one of the world’s richest men who is now most famous for running the website X, formerly known as Twitter, has a new excuse for the company’s shaky performance since he bought it last year. The problem, according to Mr. Musk, is the Jews. In an outburst on his platform on Monday, Mr. Musk claimed — without presenting any evidence — that ad revenues on Twitter are down 60 percent “primarily due to pressure on advertisers by @ADL”— the Anti-Defamation League — which he said “has been trying to kill this platform by falsely accusing it & me...