Indiana Senator Evan Bayh, a leading Democrat, has decided not to run for reelection for a third term in November, an aide said Monday, in the latest political setback for President Barack Obama.Brian Weiss, Bayh's press secretary, said the senator would make the announcement at a 2:00 pm (1900 GMT) press conference in Indianapolis, Indiana.In remarks prepared for the press conference and quoted by the Indianapolis Star, the senator cited excessive partisanship in the Congress at a time of deep economic woes as the reason for the shock decision.