Former Rep. Denny Rehberg (R-Mont.) is considering another Senate run following Sen. Max BaucusMax BaucusFive reasons why Tillerson is likely to get through Business groups express support for Branstad nomination The mysterious sealed opioid report fuels speculation MORE's (D-Mont.) retirement announcement.

"Ever since Max announced his retirement two days ago, my phone has been ringing off the hook. The encouragement I've been getting from Montanans to take a serious look at this race has been overwhelming," Rehberg told The Associated Press in a Thursday email. 

"I owe it to them, and to all the folks who I've served over the years, to keep listening and see how things develop. I'm not ruling anything out at this point."

The comments are something of a reversal for the former congressman, who lost a race to Sen. Jon TesterJon TesterSenators introduce dueling miners bills Live coverage: The Senate's 'vote-a-rama' Dems attack Trump SEC pick's ties to Wall Street MORE (D-Mont.) last fall. 

He said in January he would definitely not run for office again, and has since taken a job at a Washington-based firm.

Baucus's retirement creates a big opportunity for the GOP to pick up a seat in the GOP-leaning state. 

Former Gov. Brian Schweitzer (D) is likely the Democrats' best hope to run for the seat, and told The Hill earlier this week that he'll weigh a bid. 

Rep. Steve Daines (R-Mont.), who replaced Rehberg in the House, is also considering a bid, while former state Rep. Corey Stapleton (R) and state Sen. Champ Edmunds (R) are already in the race.

Some Republicans in the state have mentioned former Montana Gov. Marc Racicot (R) as a possible candidate, while Democrats say if Schweitzer doesn't run, EMILY's List President Stephanie Schriock (D) and state Secretary of Public Instruction Denise Juneau (D) are possible options.