The retirements have given Republicans several openings in next year's midterm elections, in which they currently need a six-seat gain to reclaim a majority they lost in the 2006 election.
Democrats immediately began courting former Montana governor Brian Schweitzer, who has honed an image as a Mountain West populist, to run for Baucus' seat. Republicans had been trying to land a top recruit to challenge Baucus, who despite his unpolished public image has repeatedly won tough re-election battles. The state's at-large congressman, Republican Rep. Steve Daines, is believed to be considering running for the open seat.
Another measure of Baucus' influence is that many of his former staffers became some of the most influential political advisers and K Street lobbyists, establishing an alumni network that is the envy of many congressional offices and the object of derision by ethics watchdogs. Jim Messina, Obama's 2012 campaign manager, rose through the ranks of Montana politics at Baucus' side.
The Baucus announcement sent lobbyists scrambling to learn who will fill the chairmanship of the Finance Committee, with its oversight of tax, trade and entitlement policy. Sen. Ron Wyden, D-Ore., a liberal with an independent streak, is next in line.
The constraints on chairmen have grown evident over the past two years, especially as Obama and congressional party leaders have strayed repeatedly into territory traditionally governed by the Finance Committee. Since January, Baucus has been in an open feud with Senate Majority Leader Harry Reid, D-Nev., and Sen. Charles Schumer, D-N.Y., over tax reform, arguing that a Democratic proposal to raise nearly $1 trillion in fresh revenue over the next decade is excessive and unworkable.
Instead, Baucus has declared his intention to work with Republicans on a rewrite of the tax code. The revised code would eliminate loopholes and deductions and use the new revenue to lower tax rates, as Republicans desire, as well as to reduce the deficit, as Democrats demand.