House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.) clashed with White House lawyers during a marathon debate over rules for the Senate impeachment trial that dragged past midnight Tuesday night.

Nadler, speaking for the first time from the Senate floor as one of the House impeachment managers, argued that Republicans and President Trump were “afraid” to let former national security adviser John Bolton testify because “they know he knows too much.”

“Ambassador Bolton is a first hand witnesses to President Trump’s abuse of power,” Nadler said, characterizing Bolton as the “tip of the spear on national security.”

Nadler added that if the Senate blocked Bolton from testifying Republicans would be participating in a “cover up.”