State Supreme Court Judge Juan Merchan cleared the courtroom Monday over a dramatic spat with the defense’s first main witness, Robert Costello, causing a period of mayhem at former President Donald Trump’s hush money trial. Mr. Costello, a lawyer who once spoke to Trump lawyer-turned-accuser Michael Cohen, seemed to take exception to one of Judge Merchan’s objection rulings, uttering “Jeez,” and then sighing, “Strike it.” “You don’t say ‘jeez.’ And you don’t say “strike it,’ because I’m the only one who strikes it,” Judge Merchan told Mr. Costello, an experienced attorney and prosecutor. He also told him not to give...