First elected to the Senate in 1978, Mr. Baucus says he wants to spend the next year and a half on Capitol Hill focused on serving his constituents and chairing the powerful Senate Finance Committee without the distraction of running for re-election.
But the veteran Democratic lawmaker, who was facing another run in 2014 in a state increasingly trending Republican, was considered one of the most vulnerable senators in his party.
“I’m not turning out to pasture because there is important work left to do, and I intend to spend the year and a half getting it done,” he said in a prepared statement. “Our country and our state face enormous challenges — rising debt, a dysfunctional tax code, threats to our outdoor heritage, and the need for more good-paying jobs.”
Mr. Baucus, a major player in getting President Obama’s health care reforms passed into law three years ago, said deciding not to run for re-election “was an extremely difficult decision.”
Mr. Schweitzer, who stepped down in January after two terms, joked last year he wouldn’t be a good fit for Congress, telling The Associated Press “I am not goofy enough to be in the House, and I’m not senile enough to be in the Senate.”
Mr. Baucus is the sixth Democrat to announce he won’t seek re-election next year, along with Sens. John D. Rockefeller IV of West Virginia, Tom Harkin of Iowa, Frank R. Lautenberg of New Jersey, Carl Levin of Michigan and Tim Johnson of South Dakota.
Democrats in the Senate will be defending 21 seats next year — seven of which were won last year by Republican presidential candidate Mitt Romney. Republicans, meanwhile, will defend 14 seats in 2014 — an advantage that has many in the GOP optimistic they can overtake the Democratic caucus’ 55-seat majority in the 100-member chamber.
President Obama thanked Mr. Baucus for his service to the people of Montana, emphasizing his work helping small businesses and the local economy in his state, and his work on a “broad range of issues” on the Senate finance, agriculture and environment and public works committees.
“Max has made small business a top priority, often taking ‘work days’ to visit local businesses across Montana and spend a day working alongside his constituents to gain perspective and help bolster the local economy,” Mr. Obama said in a prepared statement. The president made no mention of the senator’s role in shepherding his health care reform bill through the Senate.
“Max has always been a dear friend, and his decision to not seek re-election is a blow to the Senate,” said Mr. Hatch in a prepared statement. “I know I’m not the only one of his colleagues who will miss his leadership when he departs this institution.”
“It’s going to be a big loss for the Senate as an institution, as a deliberative body,” Mr. Grassley said.
• Tom Howell Jr. contributed to this article.