He also expressed confidence that he could win another term. On that the polling evidence is mixed. Recent DailyKos polls showed him leading former Congressman John Hostettler 53%-37% and former Congressman and Senator Dan Coats 55%-35%. But Rasmussen polls conducted late last month, right after the January 19 special Senate election in Massachusetts, showed Bayh trailing Congressman Mike Pence 47%-44% and leading Hostettler by only 45%-41%. Pence later said he would not run for the Senate but would run for reelection in the House. But the important point about the Rasmussen poll, as I commented when it came out, is that Bayh was running under 50% in a state where he has previously shown great electoral strength. Rasmussen did not test Bayh against Coats, who announced his candidacy in early February. Bayh expressed confidence that he could win. What these numbers tell me is that he could have won—but that he could also easily have lost.

Indiana is a state which voted Republican for president in every election between 1968 and 2004, and usually by wide margins. In 2008 it voted 50%-49% for Barack Obama—an excellent example of targeting and organizing by the Obama campaign. Evan Bayh has run far ahead of these numbers throughout his career. In 1988, having been elected secretary of state two years before, he was elected governor by a 53%-47% margin, at age 32. In 1992 he was reelected by a 62%-37% margin. After two years in the private sector, he ran for the Senate in 1998 and was elected by a 64%-35% margin. In 2004 he was reelected by a 62%-37% margin. Going into this cycle, he looked like a sure bet for reelection.

Where does this leave Democrats in the 2010 Senate contests? Not in very good shape. The North Dakota seat held by Democrat Byron Dorgan seems sure to go to Republican John Hoeven. The Delaware seat held by Ted Kaufman (appointed to replace Joe Biden) seems very, very likely to go to Republican Mike Castle. The Indiana seat held by Bayh seems now very likely to go to a Republican. The filing deadline is next Friday, February 19. Democrats do not seem to have a candidate lined up to replace Bayh. Several incumbent Democratic congressman—Joe Donnelly of the 2nd district, Brad Ellsworth of the 8th district, Baron Hill of the 9th district—mighty be plausible candidates, but none would start off with great statewide recognition, certainly nothing like Bayh’s. And a recent poll showed Hill trailing Mike Sodrel, the Republican he beat in 2002, 2006 and 2008 and lost to in 2004, in the 9th district.

Two other notes.

This has been a bad week for political dynasties, with Patrick Kennedy announcing he would not run for reelection in Rhode Island last Friday (in a quite beautiful two-minute video) and with Bayh now announcing he would not run for reelection in Indiana. Their fathers, Edward Kennedy and Birch Bayh, were both first elected to the Senate in 1962. These were victories which were taken, correctly, as signs of the popularity of the administration of John F. Kennedy. Edward Kennedy in his 47 years and Birch Bayh in his 18 years both were important members of the Senate. Kennedy won reelection eight times in heavily Democratic Massachusetts; Bayh beat three formidable Republicans, incumbent Senator Homer Capehart, to-be-EPA administrator William Ruckelshaus and Indianapolis Mayor and later Senator Richard Lugar, before losing to Dan Quayle in 1980. Patrick Kennedy and Evan Bayh surely owed their initial victories, Kennedy as state representative in 1988 at 21 and Bayh as secretary of state in 1986 at age 30, to their father’s renown. Then both made creditable political careers in their own right. Then suddenly, in 2010, both of these politicians who owed their initial rise to dynasty, decided to quit.

Second, in 1998 Dan Coats was an incumbent Republican senator from Indiana, elected in 1990 (over Democrat Baron Hill) to fill out Vice President Dan Quayle’s term and then reelected in 1992. But he decided not to seek another term in the face of Evan Bayh’s candidacy. Now Bayh, faced with Coats’s candidacy, has decided not to run. I take Evan Bayh at his word that he did not choose to retire because he believed he faced certain defeat. But he did so in the face of the toughest campaign since his first election as governor in 1988. I’m not sure that Coats is the strongest Republican candidate to replace Bayh; since his service as Ambassador to Germany in the first Bush term, he has worked as a lobbyist in Washington and registered to vote in Northern Virginia. But whoever wins the Republican nomination is likely to be the heavy favorite in a state carried by Barack Obama. It’s a tough year to be a Democrat.

View Michael Barone’s 2010 election map: Are Democrats exiting the sinking ship?