Senator Evan Bayh, a moderate Indiana Democrat, stunned politicos when he announced his retirement. Bayh is only 54, in good health, scandal-free, and looked likely to win reelection. His statement lamented "too much narrow ideology and not enough practical problem-solving." So why did he step down?

• Fighting With White House, Liberal Dems  The Atlantic's Marc Ambinder says Bayh "really grew to dislike the influence of liberal activists on his Senate colleagues. To him, these activists increased the cost of doing business. [...] When it became clear to Bayh that the White House wasn't going to play his game -- wasn't going to sell out liberals at every turn -- Bayh decided he had had enough."

• 2012 Presidential Run  The Washington Post's Chuck Lane predicts, "Quitting the Senate was a no-lose move for the presidentially ambitious Bayh, since he can now crawl away from the political wreckage for a couple of years, plausibly alleging that he tried to steer the party in a different direction -- and then be perfectly positioned to mount a centrist primary challenge to Obama in 2012, depending on circumstances."

• Revenge Against Democrats  Liberal blogger Matthew Yglesias pulls no punches. "He's ditching his seat in a manner calculated to throw control of it to a conservative Republican," he writes. "He's sad he's not going to be president? He doesn't like liberal activists? He finds senate life annoying? Well, boo-hoo. We all shed a tear."

• Furious About Estate Tax  Bayh wanted the jobs bill to include an elimination of the estate tax, and Marcy Wheeler thinks that when it didn't look like this would happen, it was "the final straw" for Bayh.

• High-Paying K Street Job Liberal blogger John Cole suspects Bayh is heading for a increased salary in the private sector. "So where is he heading? Eli Lilly? Wellpoint? PHRMA? My worst fear is he will join a wingnut welfare 'thinktank' and he will be on TV spewing his bull nonstop. At least as a lobbyist he will be doing the same damage to the country he did as a Senator because let's face it- it isn't much of a role change from what he and his wife are doing now."

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