Elon Musk is threatening a defamation suit against the Anti-Defamation League, a prominent Jewish civil rights group, saying the group’s calls for advertisers to pause their spending on the platform formerly known as Twitter were based on false accusations that have financially damaged the company. The billionaire owner of X, formerly known as Twitter, said he had no choice but to sue the group to “clear our platform’s name on the matter of anti-Semitism.” And then there are the financial considerations: Fidelity, which helped finance Musk’s $44 billion takeover, is holding its shares at a 58% discount, indicating that the...