From the moment he joined Barack Obama’s 2008 ticket as the No. 2 candidate, Joseph R. Biden Jr. has relished the dual roles of elder statesman and resident lunch-bucket American, the experienced Washington hand who has helped guide the young and cerebral Ivy Leaguers trying to run the country.

Now, the selection of Rep. Paul Ryan (Wis.) as the Republican vice presidential candidate presents a new set of challenges.

Unlike four years ago, when Biden squared off against an unknown and largely untested Sarah Palin, the vice president is competing against a longtime congressman known for being a quick-minded policy expert. Now, unlike then, Biden must defend the Obama record while, associates say, keeping an eye on a potential 2016 White House bid of his own.

As always, Biden faces the challenge of his tongue, which got him into trouble again this week when he told a racially mixed audience in Virginia that GOP presidential candidate Mitt Romney’s approach to regulating the financial industry would “put y’all back in chains.”

Obama administration officials and others close to Biden argue that his gaffes are exaggerated, that he is a man of substance who amassed enormous West Wing clout on some of the most complicated issues — managing the U.S. troop withdrawal from Iraq, pressing Obama on drawdowns in Afghanistan, and overseeing the $787 billion economic stimulus package. Advisers say they like the contrast that Biden, 69, presents against Ryan, 42. Both men stake claims to middle-class, small-town roots, and Biden associates think the vice president has a more common touch, an easier-going style, and a far greater mastery of domestic and foreign policy issues.

In recent weeks, the campaign has expanded Biden’s portfolio beyond his familiar outreach role to working-class whites, dispatching him to Hispanic and black audiences, as well, where strategists think Biden has established a connection.

“He’s able to talk in clear, personal terms,” Obama campaign manager Jim Messina said Wednesday.

Yet polls show Biden has plenty of detractors: Forty percent of Americans had a favorable view of him, according to a Pew Research Center poll this spring, while 37 percent had an unfavorable view. Romney aides say they consider Biden a disadvantage for Obama because he causes frequent distractions, such as announcing his support of same-sex marriage this spring before Obama had endorsed it.

Biden signaled Wednesday that he does not intend to rein himself in. If anything, his role in the campaign has grown since 2008; Messina pointed to the speeches Biden has given this year to groups as disparate as the NAACP, the Fraternal Order of Police, the National Council of La Raza and labor unions.

“I know I’m sometimes criticized for saying exactly what I mean,” he said in Virginia. “It’s not going to change.”

Biden was chosen for the 2008 ticket in large part because of the foreign policy heft he brought to Obama, whose national security pedigree was nearly as skimpy as those of Romney and Ryan today.

As a longtime member and two-time chairman of the Senate Foreign Relations Committee, Biden was active on issues including arms-control treaties with the Soviet Union and NATO expansion (he was for both); the 1991 Persian Gulf War (against); the 2003 U.S. invasion of Iraq (for); and the subsequent occupation and troop escalation (against).

Biden made clear to Obama that he wanted to be the “last person” in the room with the president when decisions were made. To “an extraordinary degree,” he got what he wanted, a senior White House official said.

Unless he is out of town, Biden always attends the intelligence briefing that is generally Obama’s first meeting of the day. The two are together in formal meetings “multiple times” on most days, and Biden often lingers behind, said the official, who spoke on the condition of anonymity to describe the relationship.

It became clear just weeks into the Obama presidency that Biden’s influence would extend across domestic policy, as well, when the president tapped him to oversee the unfurling of stimulus money — a process fraught with political peril.

According to the new book “The New New Deal,” whose author, former Washington Post reporter Michael Grunwald, gained access to Biden’s office, the assignment came during a weekly Obama-Biden lunch in February 2009. Biden handed Obama a memo outlining the type of person he should appoint to oversee the stimulus effort — an official with clout, people skills and the heft to call out Cabinet secretaries. Obama read the note and told Biden to get started.

Biden presided over dozens of Cabinet meetings and West Wing strategy sessions, nagging agency chiefs and phoning nearly every governor to press for swift action on stimulus spending. “He cracked a very strong whip,” Transportation Secretary Ray LaHood said Wednesday in an interview.

Biden grew irritated with liberals who chastised the administration for not securing a bigger package. “I love the left saying, ‘Well, we could’ve gotten more.’ Okay, you go get it,” Biden told Grunwald.

Associates say Biden has gained admiration for Obama as the two have gotten to know each other better — particularly since 2008, when Biden was competing for the Democratic nomination and grew frustrated with the media’s celebrity treatment of the less-experienced Obama.

“It turns out the president is a hell of a lot smarter than I thought,” Biden told a reporter in 2010.

Different styles

Obama and Biden have vastly different styles, with Biden often eager to schmooze strangers and work a room and Obama more reserved. Yet two traits Obama values in his vice president, an official said, are his loyalty and his “unique role” in challenging assumptions. Biden’s presence has proved useful during tense times at the White House.

During the administration’s 2009 debates over Afghanistan, Biden led internal opposition to the troop surge, arguing that a small ground force and air power were sufficient to conduct counterterrorism operations against the Taliban and Pakistan-based al-Qaeda. Warned about what Biden intended to say, an official said, Obama welcomed the interventions to avoid being “boxed in” by the majority of his advisers who favored escalation.

That allowed Obama to use Biden as a foil, giving the president cover to settle on a middle ground, between the troop levels backed by Biden and those pushed by others on the national security team. And although Biden may have lost the argument, the minimalist U.S. force now projected to remain after the upcoming withdrawal of combat troops is similar to his original vision.

Tasked by Obama to manage the end of the Iraq war, Biden made eight trips there in three years and helped forge the 2010 power-sharing agreement — since frayed nearly to the breaking point — that left Prime Minister Nouri al-Maliki in office.

“I’ve never seen anyone go into a room where there are disparate views and come out with everyone moving in the same direction,” said former senator Ted Kaufman (D-Del.), a longtime Biden adviser. In Iraq, Biden “went over there, and he knew the Kurds and he knew Maliki, and he was able to negotiate the whole thing.”

Biden was also Obama’s lead Senate interlocutor on the New START treaty with Russia, using his expertise and relationships to push the accord through in late 2010.

In an April speech, Biden suggested a bumper sticker for the Democrats: “Bin Laden is dead and General Motors is alive.”

Biden suggested that Romney couldn’t be trusted to have accomplished either victory. But Biden also acknowledged that he had counseled Obama not to order the bin Laden strike, a disclosure featured in a video the campaign released in March.

Critical role on trail

On the campaign trail, too, Biden has played a critical role, often making a more impassioned case for the Obama record than the president has himself. He laid out the 2012 message in five framing speeches this spring before Obama had even formally begun his campaign and will be featured during the Democratic National Convention with a prime-time introduction of the president.

Biden is scheduled to debate Ryan just once, in Danville, Ky., on Oct. 11. Former Michigan governor Jennifer Granholm (D), who played Palin in Biden’s 2008 debate preparation, said that Biden may have an easier time preparing to face Ryan.

In 2008, Granholm said, Democrats worried that Biden would appear condescending toward his younger, female opponent and come across as too much of a Beltway insider. This time, Biden will have more leeway to challenge Ryan, the House budget chairman, on Medicare, spending and other controversial subjects that have come to define the race.

Biden “does not have to mince words,” said Granholm, now host of “The War Room” on Current TV.

As for his own political future, Biden, who will be 73 during the next presidential election, has not ruled out a run. Kaufman said he expects to meet with Biden, his family and a handful of other close advisers after the November election to explore the possibility.

“He makes the final decision,” Kaufman said. “I will call for convening the group and say, ‘What about 2016?’ ”

Karen DeYoung, Nia-Malika Henderson and Scott Clement contributed to this report.