Billionaire tech mogul Elon Musk made good on a promise late Monday to file a lawsuit against Media Matters for America, the progressive watchdog he has been publicly feuding with for days. The federal suit, filed in Texas, comes on the heels of a Media Matters report that outlined how X — the platform formerly known as Twitter, which Musk now owns — is placing advertising next to hateful content. It also comes as Musk himself is under fire for antisemitic activity on his own account. The Media Matters report sparked an exodus of advertisers from X, with Musk’s lawsuit...