Senate Finance Committee chairman Max Baucus's decision to retire instead of seeking a seventh term further complicates Democratic efforts to keep control of the Senate — unless the most popular Democrat in Montana decides to take a shot at the seat.

Former Montana Gov. Brian Schweitzer is "leaning toward" running for the Senate, according to a Democrat familiar with Schweitzer's thinking.

If he runs, Schweitzer would be the early favorite. He won reelection to his second term with 65 percent of the vote in 2008, even as GOP Sen. John McCain carried Montana's electoral votes. Schweitzer also has personal wealth he could bring to the table.

Republicans haven't recruited a top-tier contender yet, though former state Senate Majority Leader Corey Stapleton and state Rep. Champ Edmunds have already declared their candidacies.