Biden is perhaps the name with the most buzz at the moment, thanks in part to his foreign policy bona fides, which were recently showcased during his high profile trip to Georgia and call for aid to the country.
"Barring a big surprise or last-minute change of heart, the choice is likely to be Sen. Joe Biden of Delaware, chairman of the Foreign Relations Committee," Howard Fineman wrote on MSNBC today. Time's Mark Halperin is also suggesting Biden will join Obama on the ticket. And Obama mentioned Biden in a speech today, further fueling speculation.
Now we are getting a preview of how Republicans might target the ticket should Biden get the nod. Earlier today, the Republican National Committee sent around a blog post from Politico's Ben Smith showing a Biden ad from 1988.
It opens with an announcer saying this: "The White House isn't the place to learn how to deal with international crisis, the balance of power, war and peace, and the economic future of the next generation. A President has got to know the territory, but that's not enough."
That sounds not unlike some of the criticism leveled at Obama, a relative newcomer to the political scene, both by Republicans and former rival Hillary Clinton. Should Biden join Obama on the ticket, it's likely that Republicans will push this line of attack – particularly since they can link it to his running mate.
Biden is also taking some heat in the liberal blogosphere. In a post yesterday, Markos at Daily Kos questioned Biden's judgment because the Delaware senator voted for the war.
"It strikes me that any pick designed to cover up a 'flaw' in Obama (i.e. 'lack of foreign policy credentials') only accentuates those flaws," Kos writes of Biden. "Make him secretary of state."
Kos also picks up on one purported problem with Biden – that his long tenure in Washington makes him a bad fit with Obama's message.
"I'd love to see him pick a fresh face in politics who reinforces Obama's message of change," he writes. "Biden doesn't."
Obama is expected to announce his running mate to supporters late Friday and appear with him at the Old State Capitol in Springfield, Illinois on Saturday.
Delaware State Election Commissioner Elaine Manlove told CBSNews.com this afternoon that Biden, who is up for reelection this year, "can run for both seats" if he becomes the vice presidential nominee.
She said the state's governor, who is sworn in on the same day as the president, would appoint a replacement for Biden should he win Senate reelection and the vice presidency. (Ruth Ann Minner, a Democrat, is presently the state's governor.) Whomever the governor appoints would serve a two year term.
UPDATE: Biden is now denying that Obama is planning to tap him. CBS News' Allison Davis O'Keefe reports that as the Delaware senator drove out of his driveway today, he leaned out slightly and said this to the reporters staking him out: "You've got better things to do guys, I'm not the guy."