Sen. Max Baucus, D-Mont., cut a $100,000 check on Tuesday to the Democratic Senatorial Campaign Committee, according to a source familiar with his campaign.

Baucus had nearly $4.9 million in his campaign account as of March 30, three weeks before announcing he would not seek a seventh term. He donated $470,000 to the DSCC last cycle, according to Center for Responsive Politics, not counting the money he raised on the committee’s behalf.

“Baucus has consistently been among the very top contributors to the DSCC, and today’s move signals that he’s continuing to be a top supporter of Senate Democrats after announcing that he won’t run again,” the source said.

His decision to retire instantly made his seat vulnerable to a Republican takeover, though potentially strong candidates from both parties still have yet to jump in. Democratic former Gov. Brian Schweitzer and Republican Rep. Steve Daines are both still looking at the race.