At issue is an incendiary aspect of special counsel Robert Mueller’s probe of Russian interference in the 2016 election: Did Trump obstruct justice by firing FBI Director James Comey or by asking Comey to go lightly on former national security adviser Michael Flynn? Mueller, who took up the Russia investigation after Comey’s ouster, seems poised to make some big decisions, including whether to ask Trump to sit for an interview, or seek a subpoena compelling the president to testify. That prospect has riled up Trump. And it has worried his legal team. They likely think little good will come if an aggressive special counsel interrogates a president with a habit of shooting off his mouth.