Paul Manafort — who took notes (apparently on his phone) during the notorious Trump Tower meeting with Russians — agreed to tell all he knows to special counsel Robert Mueller as part of a deal to plead guilty and avoid a second trial.

Why he matters, per N.Y. Times: "Of all Mr. Trump’s campaign advisers, Mr. Manafort arguably had the deepest ties to Russian operatives and oligarchs."

Manafort's cooperation may "answer some of the most critical questions about whether any Americans conspired with Russian efforts to influence the 2016 election," per the Washington Post.

• If you're keeping score: "Manafort joins four other Trump aides who have offered cooperation in exchange for lesser charges ... Michael D. Cohen, the president’s longtime personal lawyer; Michael T. Flynn, the former national security adviser; Rick Gates, the former deputy campaign chairman; and George Papadopoulos, a former campaign adviser."(NYT)