Current and former administration officials could not cite instances in which Biden's opinion has carried the day on a foreign policy decision, but they say he plays a major role in the discussions. They say he has deep knowledge of foreign affairs, personal relationships with presidents and kings, and a finely tuned sense of how the American public views foreign policy.
In his most visible act as the administration's "point man" on Iraq, he traveled to Baghdad earlier this year to deliver a tough message that if the Iraqis didn't move to political reconciliation, the U.S. would end its involvement.
In the internal debates this spring that led to the administration's new policy on Afghanistan and Pakistan, Biden joined others at the table in pushing to limit the number of additional troops in Afghanistan, and sought to focus the counterinsurgency mission more on Al Qaeda, and less on other militant groups.
A former senior U.S. official who was present said Biden, conscious of the Americans' limited patience with war, "asked a lot of questions: How much were we committing to? How many troops could all this amount to?"
Biden wanted to make sure that the administration's ambitious plans for nation building, and the military leadership's concern about the huge demands of the task, didn't lead to a classic quagmire, this official said.
"He asked the Vietnam question," he said.
Ultimately, the president opted for a troop level higher than Biden had advised.
Biden associates say his relationship with Obama is evolving. Coming to the political partnership with no real friendship to speak of, Biden has sought to cultivate one with Obama since the swearing-in. A Biden aide calls the process a "courtship after the marriage."
One White House official recalls the vice president fretting over what to get Obama for his 48th birthday earlier this month. Biden wanted to go with a Nintendo Wii. Told that Obama's daughters already have one, a disappointed Biden said, "You're kidding." Instead, he went with a golf range-finder to help the president judge distances to the hole.
Biden's practice is to do what he's asked. He has traveled frequently to battleground states important to Obama's reelection. Travel records show he has spent five days in Pennsylvania; a total of six in Colorado and North Carolina; and four in Virginia.
A comparison to other vice presidents shows Biden taking on a larger role than some high-profile Democratic predecessors. There is no comparison to George W. Bush's vice president, Dick Cheney, whose broad portfolio made him a virtual co-president. But one could argue that Biden is more influential than Al Gore, whose primary assignments -- reinventing government and global climate change -- were not necessarily at the heart of Bill Clinton's agenda.
Gore did not interview Supreme Court candidates. Biden did. As a former Senate Judiciary Committee chairman who has presided over volatile nomination hearings, Biden also spoke informally to Sonia Sotomayor about what she might expect in her star turn before the panel.
Biden's ambitions go beyond serving as an influential vice president. He doesn't necessarily believe his political career has peaked.
Aides said he might go for the Democratic presidential nomination in 2016. He would be 74 upon taking office, but his staff insists that's not too old.
"He's incredibly fit, vigorous man of his age, and it's impossible for me to imagine that he won't be in public service in 2017 in some form," a Biden aide said.
Times staff writers Mark Z. Barabak in San Francisco, Richard Boudreaux in Jerusalem, Megan K. Stack in Moscow and Borzou Daragahi in Beirut contributed to this report.