"Highly overrated," said Mike Murphy, a Republican who was a senior adviser in McCain's 2000 campaign.
The GOP nominee-in-waiting is in the final stages of deciding who should join him on the ticket, and Obama's selection of Biden - a savvy debater, willing attack dog, and blue-collar champion - is certain to figure into McCain's calculation.
His short list of contenders reportedly includes former Massachusetts Gov. Mitt Romney and Minnesota Gov. Tim Pawlenty, as well as former Pennsylvania Gov. Tom Ridge and, perhaps, Democrat-turned-independent Joe Lieberman of Connecticut. A dark horse pick - like Gen. David Petraeus or former Secretary of State Colin Powell - also is possible when McCain announces his choice, perhaps as early as Friday.
McCain's upcoming schedule is fueling speculation. He is to appear at a rally in Ohio on Friday, and another in Washington, Pa., on Saturday - that one with Ridge. As McCain deliberates, Pawlenty and Romney are in Denver playing the role of top surrogates.
"Obama has picked someone who is going to be very aggressive in going after McCain, and who is not going to be recalcitrant about it," said Steve Elmendorf, a deputy campaign manager for Democrat John Kerry in 2004. "If I was McCain, I'd be thinking about my own attack dog."
Added John Feehery, a Republican and ex-aide to former House Speaker Dennis Hastert: "He's going to want someone who can go toe to toe with Biden."
For months now, McCain has had to do double duty, casting himself as the tested experienced leader while at the same time criticizing Obama as unqualified for the Oval Office. A tough-talking vice presidential nominee would free McCain to focus largely on his first task.
Romney, who challenged McCain with zeal during the GOP primary, and Ridge, who as a McCain surrogate assailed Romney during the primary, both have shown a talent for the requisite biting rhetoric.
At the same time, strategists say McCain should consider how his running mate will stack up against Obama's in the vice presidential debate this fall. It's arguably the most visible role vice presidential nominees play in the race, and Biden is a deft performer with deep knowledge of policy, both foreign and domestic.
Here, too, Romney stands out. He consistently had solid showings during numerous GOP debates.
Still, that's not to say any of the others wouldn't rise to the occasion.
"Certainly Biden was a big choice for Obama, and it does, therefore, force McCain to think about a big choice, both in terms of debates and the potential demographic or state-by-state advantages in who he picks for his running mate," said Bob Shrum, a Democrat and veteran of many presidential campaigns.
Obama's campaign hopes Biden, with his Catholic, working-class, Pennsylvania roots, proves to be an asset in key swing states and among core voting groups. They also hope his foreign policy, crime-fighting, 36-year Senate resume will help reassure voters wary about Obama's readiness to be president.
Biden is the senior senator from Delaware, a longtime Democratic voting state that Obama is certain to win. However, he's also a native of Scranton, Pa. He has been dubbed "Pennsylvania's third senator" because of his ties to the battleground state and his exposure in the Philadelphia media market that reaches Delaware.
Republicans - and even some Democrats - cast doubt that Biden on the ticket will seal Pennsylvania for Obama, but they say he may help some. Likewise, Obama's campaign hopes Biden gives Democrats an edge in Midwest states like Michigan, Ohio, Wisconsin and Iowa that are home to the same types of voters.
"Biden is a blue-collar, pro-union attractive candidate," said Scott Reed, a Republican who ran Bob Dole's campaign in 1996. "Republicans are going to need to counter that."
McCain has several options to offset Biden's strengths, both in terms of states and demographics.
He could put Ridge, a former Pennsylvania governor who backs abortion rights and connects with the working class, on the ticket, or choose Romney to try to help in Michigan, another Democratic-leaning state where McCain hopes to prevail and one where Romney grew up and still has deep ties.
Pawlenty might be able to help in Minnesota but Republicans say the state will be tough for McCain to win even if the governor is on the ticket. Still, Pawlenty could help counter Biden's blue-collar biography; he, too, came from a modest background and calls himself a "Sam's Club" Republican.
Republicans and Democrats alike say McCain also would be wise to choose someone who is strong where he is weak - such as on economic issues - to try to undercut the opposition's attacks.
Obama sought to do that with his Biden pick.
Said Steve McMahon, a Democrat who was a senior aide on Howard Dean's 2004 campaign: "Obama has effectively checked McCain on McCain's only relevant argument by choosing Biden, who has more foreign policy and Washington experience than McCain."