Senate Minority Leader Chuck Schumer started the Senate impeachment trial negotiations by sending Majority Leader Mitch McConnell a letter with an offer on the parameters, including a request for testimonies from former national security adviser John Bolton and acting White House chief of staff Mick Mulvaney.

In his Sunday letter, Schumer proposed that McConnell call both Bolton and Mulvaney, along with associate director for national security Michael Duffey and Robert Blair, a senior adviser to Mulvaney, to testify. All four requested witnesses have direct knowledge of the Trump administration’s withholding of aid to Ukraine and of the Russia investigation origins.