Who would be the best choice to replace Biden and why?

[Mister Mets]

They wouldn't pick Warner because they need his Senate Seat. Unless theirs a law in Virginia that says you must appoint someone of the same party, McDonnell would either appoint himself or another GOPer. They'd probably pick Bayh and pick of Indiana's 11 votes. They could go for a wildcats like John Hickenlooper and close out Colorado against Romney.
But we all know it ain't happening.

It's always a bad idea for a Governor to appoint himself to the Senate. But McDonnell would be happy with the opportunity to resolve the Gubernatorial primary, by appointing either the Attorney General or the Lieutenant Governor to Warner's Senate seat.

Bayh would be a smart choice, because he has nothing to lose and wouldn't endanger any seat. But it's not clear he's an effective campaigner. And he complained a lot about Democrats recently.

Cuomo would have the resume, as a big-state Governor and former Cabinet member.

I suspect that anyone planning a 2016 run would be unhappy, since whoever Obama chooses would become the favorite. Aside from Hillary Clinton, who is already the favorite, should she run. But there would be less incentives for her to accept.

Leon Panetta could be an interesting choice, as an elder statesman with a fantastic resume and lots of foreign policy experience. That helps provide a contrast with Romney/ Ryan. And there would be no concerns that he would seek the nomination in 2016.

Angus King might be a game-changer. As a former Independent Governor, he would have a lot of credibility. And the Democratic candidate would become the favorite in the Senate race.

[HagridOfTheDeep]

Hillary Clinton is the obvious choice here. 

I agree. The interesting thing is, the roles have reversed since 2008. Clinton would actually overshadow Obama on the ticket.

[milhouse24]

I like the Leon Pannetta suggestion.  Plus he could deliver a lot of Italian-Catholics, unlike Andrew Cuomo's more aggressive style. 

I say its at least a 75% chance they are considering replacing Biden. 
Its more common than not that VP's are replaced.  Perhaps not within the past 50 years, but Ford replaced his VP with Dole at the convention. 
FDR went through a lot of VP's. 
There are a variety of reasons for wanting to replace a VP, but I think "Old Age" is simply the best reason that no voter will argue with. 
Its not a question of competence, but most voters simply want the best energetic tickets capable of getting things done. 

If Obama can find someone who is competent, capable, and can secure a swing state, then he should replace Biden.  He may actually get a bump in the polls, if people prefer his new VP. 

[Brittain33]

I say its at least a 75% chance they are considering replacing Biden. 

I say there's close to a 100% chance Al will be posting a two-sentence follow up to this post.

[Lincoln Republican]

Presidents who have replaced their Vice Presidents or have had their Vice Presidents replaced for them

Thomas Jefferson-Aaron Burr, George Clinton
James Madison-George Clinton, Elbridge Gerry
Andrew Jackson-John C. Calhoun, Martin Van Buren
Abraham Lincoln-Hannibal Hamlin, Andrew Johnson.  
(Tough luck for Hamlin.  He would have become President)
Ulysses S. Grant-Schuyler Colfax, Henry Wilson
William McKinley-Garret Hobart (died in office), Theodore Roosevelt
Franklin D. Roosevelt-John Nance Garner (first two FDR terms), Henry Wallace (third FDR term), Harry Truman
(Tough luck for Wallace.  He would have become President)
Richard Nixon-Spiro Agnew (resigned), Gerald Ford
(Tough luck for Agnew.  If he wasn't a crook he would have become President)
 

[True Federalist (진정한 연방 주의자)]

Presidents who have replaced their Vice Presidents or have had their Vice Presidents replaced for them

Thomas Jefferson-Aaron Burr, George Clinton
James Madison-George Clinton, Elbridge Gerry
Andrew Jackson-John C. Calhoun, Martin Van Buren
Abraham Lincoln-Hannibal Hamlin, Andrew Johnson.  
(Tough luck for Hamlin.  He would have become President)
Ulysses S. Grant-Schuyler Colfax, Henry Wilson
William McKinley-Garret Hobart (died in office), Theodore Roosevelt
Franklin D. Roosevelt-John Nance Garner (first two FDR terms), Henry Wallace (third FDR term), Harry Truman
(Tough luck for Wallace.  He would have become President)
Richard Nixon-Spiro Agnew (resigned), Gerald Ford
(Tough luck for Agnew.  If he wasn't a crook he would have become President)
 

Of these, the only one who was dropped to improve the electoral prospects of the ticket was Hamlin.

Burr, Calhoun, and Garner had a falling out with their President.
Clinton and Hobart died in office.
Colfax and Agnew were caught up in scandals.
Wallace was dropped because the 1944 election was unusual.  The party leaders knew that FDR would not last out his fourth term and they didn't want Wallace to inherit the Presidency.

[Politico]

Folks, I think we can drop this speculation. Biden's reaction to being dropped would probably be on par with this (except at the presidential level, obviously):

http://www.youtube.com/watch?v=gW1lnA6f4E0

The fallout from dropping Biden would create a legacy of Obama losing 40-45 states. I mean, maybe they could pull it off with Hillary Clinton. But I doubt it. Biden is not the type to go out with a whimper, and the blowback would be unfathomable.

[Brittain33]

Right, so in the last 100 years it only happened by choice with FDR, after two terms, when big parts of his party were in open revolt over the incumbent.

[milhouse24]

At least with EAgleton, doctors proved he was mentally crazy. 
As far as I know, no doctors have concluded Biden is mentally unstable or going through dementia. 

If Biden fell off a stage and broke his leg, like Bob Dole in 1996, then that would open up some consideration from party leaders to replace him. 

Even with Dick Cheney's massive heart problems, I'm sure Karl Rove had replacement candidates ready and vetted for immediate announcement, were Cheney to become incapacitated.  I'm sure Axelrod has a list ready and vetted in case something happens to Biden.  Its the most logical and rational and responsible thing to do given the stakes.