The comments came on the heels of a report in The Hill earlier on Thursday that said Messina had received calls in the last day from "high level" officials in Montana asking if he would serve as a placeholder for the senator, according to a source familiar with the conversations. Obama is asking Baucus to serve as U.S. ambassador to China.
"No US Sen. appt for me," Messina wrote in the tweet on Thursday afternoon.
Messina, who launched a consulting group since the 2012 campaign, also wrote that helping Obama and growing his own firm "is my focus."
The Montanan was said by sources to be influential in Obama's decision to nominate Baucus as envoy to China. Speculation on Gov. Steve Bullock's appointment centered on Lt. Gov. John Walsh, who is running to succeed Baucus.
But after news reports surfaced late Wednesday, Messina received queries about whether he'd be willing to serve as placeholder in the Senate in the event that Gov. Steve Bullock decided not to appoint Walsh, according to the source.
The source said Messina seemed "very surprised" by the calls asking if he might consider the possibility.