Baucus had already announced plans not to seek reelection when President Obama tapped him in December for the new role. The appointment will allow Montana's Democratic governor to choose a new senator. It is widely assumed that Baucus's successor would run for the seat in November as an incumbent, with the hope of helping Democrats hold on to a narrow majority in the Senate.
As chairman of the powerful Senate Finance Committee, Baucus played a key role in crafting Obama's health-care law and was among the first Democrats to publicly fret about the law's implementation -- worries that later turned out to be well-founded.
Baucus’s impending departure will set off a round of musical chairs among Senate committee chairmen. Sen. Ron Wyden (D-Ore.) is expected to assume control of the finance panel, a move that likely will lead to Sen. Mary L. Landrieu (D-La.) taking the top spot on the Senate Energy Committee.