Bayh's Withdrawal: A Conjecture
The news stories I have seen on Indiana senator Evan Bayh's decision not to run for reelection have mostly focused on the decision, not the timing, although they usually mention that, by leaving it to the last minute, he made it almost impossible for anyone to collect the signatures required to enter the primary. Nobody seems to be asking why he did it that way.
One interesting possibility occurs to me. Perhaps he believed that an earlier announcement would result in a bruising primary fight and the probable winner would be a candidate unlikely to win the election—roughly speaking, what happened to the Republicans not long ago in a New York congressional district. Resigning only a few days before the deadline for the primary throws the choice to the state democratic committee—which can, and perhaps will, pick the strongest candidate.
I should add that I know very little about Indiana state politics, so this is only a conjecture. Perhaps some better informed reader can tell me if it is a plausible one.