I started watching politics in 1950 and I have a long memory and can see a big picture. Right now I'm seeing how few years Democrats have held the White House, and hoping this year we nominate someone who can win it again.
Since LBJ it's been: 1972 Nominate McGovern, get Nixon. 2000 Support Nader, get Bush Jr.
Let's not have: 2008 Support Obama, get another Bush.
Obama is young enough to try again later. Gore (who got the popular vote in 2000) isn't interested. Bill and Hillary will be too old soon, so maybe best to use them while we've got the chance. They ARE the only Dems who got re-elected in the last many decades.
As for Obama, his chances will be better later, when he's got more credentials and isn't running against someone as popular as the Clintons. And if the Dems have had SOMEONE in the White House cleaning up the election process (and no more GOP foul-ups and fascism in the meantime).