Mr. Manafort, installed as the chief strategist for Mr. Trump's campaign after the firing of his original campaign manager, handed in his resignation Friday.

Paul Manafort, installed as the chief strategist for Donald J. Trump's campaign after the firing of his original campaign manager, handed in his resignation on Friday morning.

Mr. Manafort left after a major shake-up following a New York Times report about tumult within the Republican presidential nominee's campaign. His departure reflects repeated efforts to steady a campaign that has been frequently roiled by the behavior of its tempestuous first-time candidate.

He was also dogged by reports about secretive efforts he made to help the former pro-Russian government in Ukraine, where he has worked on and off over several years. He had also been viewed with trepidation by Jared Kushner, Mr. …