Former Rep. Denny Rehberg (R-Mont.) is considering another Senate run following Sen. Max BaucusMax Sieben BaucusBernie Sanders flexes power on single-payer ObamaCare architect supports single-payer system Trump has yet to travel west as president 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 TesterJonathan (Jon) TesterOvernight Cybersecurity: Equifax security employee left after breach | Lawmakers float bill to reform warrantless surveillance | Intel leaders keeping collusion probe open Overnight Finance: White House requests B for disaster relief | Ex-Equifax chief grilled over stock sales | House panel approves B for border wall | Tax plan puts swing-state Republicans in tough spot Senators grill ex-Equifax CEO over stock sales 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.