John Dowd, the lead lawyer representing President Donald Trump in the special counsel’s Russia investigation, left the legal team on Thursday partly because of the hiring of a new attorney who is expected to take a more confrontational approach, two people close to the team said.

Mr. Dowd’s resignation stunned some of Mr. Trump’s advisers, who weren’t expecting him to depart at a phase of the investigation that involves sensitive dealings with special counsel Robert Mueller.

...