That, perhaps more than any other factor, was more than Bayh could handle. While he has had a meteoric political career in the Hoosier state, Indiana remains a swing state that Obama only narrowly carried in 2008, but whose political grassroots are still basically conservative and still leans Republican.
He tried to cover his left-leaning flank with potshots at the partisan warfare that has engulfed Congress, pointing to Republicans who supported a proposed deficit reduction commission bill but turned against it when it came up for a vote. In fact, the GOP lawmakers couldn't stomach the idea of a group of unelected commission members proposing to slash the deficit by raising taxes on an economy still flat on its back.
In the end, Bayh, who rarely led on any controversial issues, admitted he didn't have the fire in his belly to fight for his own seat or for what he believed in the legislative arena. "After all of these years, my passion for service to my fellow citizens is undiminished. But my desire to do so by serving in Congress has waned," he said.
Nonetheless, Bayh's decision came as a shock to his party and to his closest colleagues, who had expected him to run. Just days before his withdrawal, senior aides and Democratic state chairman Dan Parker were telling reporters that he was on course for another campaign.
On Capitol Hill, Democrats were shaking their heads in disbelief at the number of Democratic incumbents and potential candidates who were dropping out of contention.
First came Connecticut Sen. Chris Dodd, then Byron Dorgan of North Dakota, then Delaware Attorney General Beau Biden -- Vice President Joe Biden's son, who shocked Democrats when he passed on running for his father's Senate seat.
Bayh's desertion follows the upset in Massachusetts where Republican Scott Brown won the late Sen. Edward Kennedy's seat. The midterm election races have barely begun, and yet the GOP seems to be scoring one tactical victory after another by driving Democrats from the field.
The two open seats in Delaware and North Dakota are now described as "solidly Republican" by election forecaster Charlie Cook. And five more Democratic seats are considered toss-ups, at best, or leaning Republican: Arkansas Sen. Blanche Lincoln's; Colorado Sen. Michael Bennet's; Obama's former seat in Illinois; Senate Majority Leader Harry Reid's in Nevada; and Arlen Specter's in Pennsylvania.
If Republicans win the eight Democratic seats the Cook Political Report lists as solid, likely or leaning Republican, hold on to their own four open seats, and pick up a couple of wildcard seats, they would have a 51-seat majority.
Right now, this seems like an improbable stretch for the Republicans, but so was winning Ted Kennedy's seat in heavily Democratic Massachusetts.