A key pickup opportunity for Republicans, especially if the strongest Democrat candidate decides not to run.

Breaking news, from the Washington Post:

Senate Finance Committee Chairman Max Baucus (D-Mont.) is retiring rather than seek re-election in 2014, according to two senior Democratic strategists familiar with his plans. First elected in 1978, Baucus has been the top Democrat on the powerful committee since 2001. The likely Democratic candidate to succeed him would be former governor Brian Schweitzer, sources said.

Baucus is one of the principle perpetrators of ObamaCare, but he recently made headlines by warning that implementation threatened to become a “huge train wreck.” He’s also in some hot water with the Left for refusing to climb aboard the gun-control bandwagon, as chronicled by USA Today:

The Progressive Change Campaign Committee (PCCC) is running full-page ads in seven newspapers throughout Montana. The ad includes the signatures of 75 gun owners across Montana who are protesting Baucus’ vote. “Senator Baucus, it was WRONG to vote ‘no’ on stopping gun violence. 79% of Montana voters support background checks. Stand with us, not gun manufacturers,” the ad text says. “Support sensible gun laws and keep our families and communities safe.” The group intends to spend $100,000 targeting Baucus and Sens. Mark Pryor of Arkansas, Mark Begich of Alaska and Heidi Heitkamp of North Dakota. All but Heitkamp are up for re-election in 2014. Baucus summed up his reason for voting against the gun proposal in one word. The senator said in a statement that Montanans told him “they are overwhelmingly opposed to new gun-control laws.”

NBC News notes that Baucus’ decision not to seek re-election may impact a 2014 electoral map that was already looking tough for Democrats:

Baucus’ decision gives Republicans a key pick-up opportunity in Montana — where President Obama won just 42 percent of the vote in 2012. However, a Democrat familiar with Democratic Gov. Brian Schweitzer’s thinking says the governor is leaning toward running for Baucus’ seat, which would give Democrats a solid chance at holding onto the seat. So far this cycle, six Senate Democrats have announced they won’t seek re-election — Baucus, Tom Harkin of Iowa, Tim Johnson of South Dakota, Jay Rockefeller of West Virginia, Carl Levin of Michigan, and Frank Lautenberg of New Jersey. And two Republicans have announced their upcoming retirements — Saxby Chambliss of Georgia and Mike Johanns of Nebraska.

There will probably be a lot of pressure on Schweitzer to get into the race, if he’s seen as the best candidate to hold the seat for Democrats. Even so, it sounds likely to be a tough race that will consume a lot of political resources.