Updated 12:42 a.m. | Montana Sen. Max Baucus has decided to retire instead of seek re-election next year, a sudden move that caught many colleagues and state Democrats off guard.

Democratic sources confirmed the news to CQ Roll Call on Tuesday morning — after which Baucus told reporters he was working to spread word to his staff.

Now that Baucus is exiting after this congress, Roll Call contributing editor Stuart Rothenberg rates this race as a Tossup in the Rothenberg Report.

Former Montana Gov. Brian Schweitzer will be at the top of Democrats’ wish list as the candidate in the open-seat race. A Democratic source indicated the ex-governor is leaning toward running.

The retirement also opens up the Finance gavel come 2104. Sen. Ron Wyden, D-Ore., is next in line for that post, and Democratic sources indicated he would be likely to take it.

Democratic Senatorial Campaign Committee Chairman Michael Bennet made no mention of Schweitzer in a statement released Tuesday morning.

“Democrats have had a great deal of electoral success in Montana over the last decade, and I am confident that will continue,” Bennet said. “Democrats built an unprecedented ground game in Montana in 2012 when Senator Tester was re-elected, and we will continue to invest all the resources necessary to hold this seat.”

Senate Republicans, meanwhile, characterized Baucus’ retirement as a sign “the 2014 electoral map is in free-fall” for Democrats.

“Vulnerable Democrats will face voters just as Obamacare’s tax hikes, mandates, fees, penalties and red tape bureaucracy take shape over the next eight months, and Senator Baucus’ retirement reflects that political reality,” said National Republican Senatorial Committee Executive Director Rob Collins. “The 2014 electoral map is in free-fall for Democrats, who were already facing a daunting challenge.”

Republicans must net six Senate seats to win control of the chamber in 2014. However, Senate Democrats face a difficult map and must defend seven seats — including Montana — in states President Barack Obama lost last year.

The Washington Post first reported the Baucus retirement.

Meredith Shiner contributed to this report.