During the hard-fought primaries last spring, Barack Obama swooped in from the campaign trail for a brief stop at the Senate hearings on Iraq. With Gen. David Petraeus and Amb. Ryan Crocker giving testimony before the Foreign Relations Committee, it was one of those rare moments when the spotlight panned back to Washington. And Obama didn't disappoint. Even with all the distractions of taking on Hillary Clinton, Obama asked one of the most penetrating questions of those two days of hearings: How much of an Iranian and Al Qaeda presence in Iraq would be acceptable before we would leave? Both Petraeus and Crocker seemed caught by surprise by this realpolitik reckoning, and Obama received kudos in the media for his smarts. Even Petraeus acknowledged that Obama was "exactly right" in saying that the most the United States could achieve was not to wipe out Al Qaeda entirely but to leave behind a "manageable situation."

What was not reported at the time was that Obama's line of questioning was suggested to him by Sen. Joe Biden, the Committee chairman who had quietly become one of the Illinois Democrat's main foreign-policy consiglieres after abandoning his own presidential bid. "I discussed with Sen. Obama how to proceed with Petraeus and Crocker," Biden told me in late May. "He asked for my advice."

This week, Obama's choice of Joltin' Joe Biden as his vice-presidential running mate, particularly coming after the tenure of perhaps the most powerful veep in U.S. history, Dick Cheney, raises a few serious questions. First, is Obama really as confident about his commander-in-chief and foreign-policy credentials as he says he is? During his now-infamous remarks to a San Francisco fundraiser last spring, Obama cited his international upbringing and travels and declared that "foreign policy is the area where I am probably most confident that I know more and understand the world better than Senator Clinton or Senator McCain." His pick for veep, Obama added back then, would likely be "somebody who knows about a bunch of stuff that I'm not as expert on." The Biden choice, however, would seem to suggest otherwise—or at least that Obama believes he has a public-perception problem on foreign affairs.

A second, related question: To what degree will the combative and assertive Biden be a behind-the-curtain influence on Obama's foreign policy as much as an attack dog on the campaign trail? In some respects, Biden is the anti-Cheney. He's a garrulous glad-hander while Cheney is reticent and secretive; he's a sunny champion of diplomatic engagement while the vice president is known for his dark, Hobbesian view of the world. Though he is not averse to the use of force—Biden was one of the first Dems to urge Bill Clinton to intervene in the Balkans in the early '90s—he could not be more different from Cheney in personality or global outlook. But in one respect the Delaware Democrat and the Wyoming Republican resemble each other: like Cheney, Biden is confident to the point of cockiness in pushing his foreign-policy views, and like the current veep he knows how the levers of power work in Washington.

Make no mistake: Obama has always been his own man on foreign policy. During his very first appearance on the Foreign Relations Committee, at Condi Rice's confirmation hearings in January 2005, he made the steely secretary of state-to-be squirm by asking sharp questions about the readiness of Iraqi troops, impressing Biden and other Senate veterans. A little over a year ago, in a defining speech on counterterrorism at the Woodrow Wilson Center in Washington August 2007, Obama became one of the first senators to call for additional brigades to be sent to Afghanistan—the "real war"—and to substantially increase non-military aid. Biden has echoed him. Obama also anticipated what later became U.S. policy by calling for unilateral strikes inside Pakistan.

But Biden's long record of counseling deep engagement in trouble spots and pushing nuanced, intensive diplomacy—especially talking to enemies—conform in many ways to Obama's world view. In an interview with me in late 2004, Biden sketched out what later became Obama's own position on Iran, saying that Bush should open up direct diplomacy with Tehran "because he has no alternative. The terms [of the talks] should be wide open. This administration spends too much time arguing over the shape of the table. They don't get anything done." He also insisted that Bush open up bilateral talks with North Korea—which the administration later reluctantly did. If Obama and Biden win, it is easy to imagine that they could enjoy something like the one-on-one rapport that George W. Bush is said to have with Cheney.