Sharon LaFraniere and Kenneth P. Vogel:

Mr. Manafort’s decision, announced at a federal court hearing in Washington in which he pleaded guilty to two conspiracy charges, was likely to unsettle Mr. Trump, who had praised Mr. Manafort for standing up to prosecutors’ pressure and had hinted that he might pardon him.

It is not clear what information Mr. Manafort offered prosecutors in three days of negotiations that led to the plea deal. But in court on Friday, Mr. Manafort agreed to an open-ended arrangement that requires him to answer “fully, truthfully, completely and forthrightly” questions about “any and all matters” the government wants to ask about.

He’s also the first cooperating witness from the infamous Trump Tower meeting in 2016 that alleged dirt on Hillary Clinton.