The suit said a nondisclosure agreement that accompanied the payment was not valid.After filing the suit, Mr. Avenatti became a regular on television, often commenting on Mr. Trump. But he eventually ran afoul of the law. He was indicted and later convicted on charges that he tried to defraud Nike for millions of dollars and was charged separately in the case involving Ms. Daniels.Although a criminal defendant has the constitutional right to represent himself, legal experts said, that right is not absolute once a trial begins, and a judge must weigh the defendant’s interest against other interests, like the potential disruption a mid-trial switch can cause.Stephen Gillers, a professor at New York University School of Law, said the fact that Mr. Avenatti is a lawyer and represented himself in the California trial most likely made it easier for Judge Furman to allow him to take over his defense.“Furman can conclude that, ‘Well, I’ve got a competent defendant here. I don’t have to worry about him messing up. If he does mess up, it’ll be his own fault. And meanwhile, if I deny Avenatti’s request, I’ve created an appellate issue if he’s convicted,’” Professor Gillers said. Rebecca Roiphe, a professor at New York Law School, noted that Mr. Avenatti, because of his combative personality, could face real hurdles when he cross-examines Ms. Daniels.“It’s something that I think jurors are certainly going to be paying attention to,” Professor Roiphe said, “because rather than seeing a lawyer up there talking to a witness, it’s almost like you have two adversaries in a ring.“I would certainly advise him, if I were his friend, his colleague, his lawyer, not to do this because I think it’s just too risky,” she said. “There’s just a way in which it seems to me more likely that it will end up backfiring for him than serving his interests.”Benjamin Weiser contributed reporting.