Senate Minority Whip John Thune (R-SD) transferred $4 million to the campaign arm of Senate Republicans on Tuesday, the latest in a battle over who will succeed Sen. Mitch McConnell (R-KY) as GOP leader.

The transfer, announced during a lunch hosted by Sen. Steve Daines (R-MT), the chairman of the National Republican Senatorial Committee, is the largest in the organization’s history. Thune also set the previous record, $2 million, in 2016.