There are plenty of scenarios where Obama decides he can't run. God forbid there's a personal tragedy in his life, or he suffers from something degenerative that won't immediately debilitate.
As for Clinton, if she wants to be president at all, she probably has to jump in the race in 2012. Otherwise she's likely waiting until 2020, which is probably too late to start a first term.
Obama's legacy ITTL is in better shape than it'll likely be in 2016 IOTL. Four years of weary fighting with no result has disappeared, and the sympathy of the country will shift towards him.
This means his endorsement has greatly added weight.
He might be able to avoid endorsing Biden or Clinton ("both did so much for my administration" is the tag line.) But the press will treat that as a slight to Biden, definitely the closer and more loyal of the two.
If he does endorse Biden- and remember his endorsement means a LOT more ITTL- we've potentially got a real fight on our hands.
Clinton's got less of a built-in advantage (4 less years to get her machine back together) but Biden can't capture all of Obama's juice, either.
Honestly, Obama's endorsement probably makes the fight too even. Both would be too strong and well-funded to drop out before at least a few primaries, and that only serves to weaken the party, and more importantly, Obama's legacy.
Since Obama's got potential control over the outcome if he DOESN'T endorse Biden, he probably talks Biden out of running. He couldn't talk Clinton out of running, so it's got to be Biden. If he does nothing, Biden ends up looking weak and Obama ends up looking disloyal. And as I said before, if he endorses Biden, everyone ends up looking weak.
So getting behind Clinton's what the smart political money is on.
The Republican field could be a lot stronger in terms of better conservative candidates running. They will still have a strong fight on their hands all through the primaries.
Cruz or Rubio is my guess. A surprise from Christie's an interesting possibility, but we're still talking about the Republican primaries here, and I am skeptical he can win under any circumstances.
Clinton would have a very tough fight. The PAC money would rain down hard on all the culture war touchstones she embodies. There's less traction for attacking Biden, but he's also less impressive a candidate. I still think he's solid enough, and the field is tilted enough towards the Democrats (even with a conservative voter bump for Rubio or whoever) that Biden would definitely win.
Clinton...could stumble. Lots of pressure, lots of attacks, not honestly all that charismatic either. It's still a Democratic year for the presidency and it's her's to lose, I just think she's more likely to lose than Biden. To put it another way, I'd give her 3::2 odds and Biden 2::1 odds.
And of course this assumes Obama announces his decision with plenty of time. If this happens right around the convention, the Republicans are stuck with Romney and Biden gets the nomination, possibly with a floor challenge at the convention from Clinton, if she wants to mount one. Whoever wins, big advantage to the Democrats- sympathy mounts in their cause and Romney remains unimpressive.
