Before becoming vice president, Joe Biden declared his intention to “restore the balance” between his office and that of the president. In his view, Dick Cheney had essentially created a separate power base, nearly independent of the Oval Office. Biden’s vice presidency was going to restrain those impulses. He would integrate his role and staff more smoothly and fully with the White House, more in the style of Walter Mondale during Jimmy Carter’s presidency and, to a degree, Al Gore in the Clinton years.

But Biden has hardly taken a back seat. Instead, he has become President Obama’s workhorse on issues from war to budgets to economic recovery. The New Deal Democrat from coal-country Scranton has even become a liberal standard-bearer on same-sex marriage, nudging the president to publicly shift positions. While Gore was given unusually significant responsibilities on very specific areas such as the environment and government efficiency, Biden, much like Cheney before him, has had plenty of running room on an array of key administration policies — a sort of de facto assistant president.

Unlike the grim Cheney often shunted to undisclosed locations, however, Biden has been a visible sidekick to Obama — enough to keep speculation alive about his presidential aspirations for 2016.

In nearly four years as vice president, Biden has been the chief monitor of the economic recovery efforts, coordinating federal projects with mayors and governors. As Obama’s emissary to the Republican congressional leadership during the 2011 debt-ceiling negotiations, he was nicknamed the “McConnell whisperer” by aides, according to Bob Woodward’s new book. And he has overseen the U.S. military and reconstruction agendas in Iraq and Afghanistan, while encouraging Obama to hold fast to the troop-withdrawal timelines Biden has advocated since taking office — a point he emphasized repeatedly in his debate with Rep. Paul Ryan (R-Wis.) on Thursday night.

While Biden showed distracting, Gore-like flashes of irritability toward Ryan, he filled in blanks that Obama had left unspoken in his own debate with Mitt Romney, and he brought the discussion back to the Democrats’ standard defense of the middle class. In so doing, he provided a tonic his party needed after the president’s flat performance.

Although Obama and Biden were not close in the four years they overlapped in the Senate, according to Obama strategists David Axelrod and David Plouffe, their candidate was impressed with Biden in the 2008 Democratic primaries. After he delivered uncommonly pithy answers in debates, other contenders onstage would begin their responses with variations of “Joe is right.” And in a South Carolina debate, when asked whether he could control his wagging tongue, Biden’s straight-faced, one-word answer — “Yes” — brought the house down.

While he may have caused the Obama team some anxiety in the general-election campaign with his freewheeling style, the running mates meshed quickly. Early on, Obama publicly called Biden the best vice president to date and told him he wanted him on the ticket again in 2012.

As Obama decided in late 2009 to acquiesce to the generals’ pressures for a troop surge in Afghanistan, Biden played house skeptic in ways that eventually helped tilt administration strategy back toward counterterrorism, even as counterinsurgency remained the stated policy. In doing so, he retained his standing with the Democrats’ liberal wing, which increasingly chafed at Obama’s pragmatic bent.

Although he reportedly caught some flak from the Oval Office for blandly observing on a Sunday morning talk show this year that he had come around to supporting same-sex marriage — preempting a similar planned statement by Obama on the issue — he ended up boosting the president’s ratings among female voters in particular.

In the current campaign, Biden has continued to be the administration’s best envoy to the old Democratic constituency that suffered serious erosion in the Reagan era. After Bill Clinton’s eight White House years, it slipped back into decline, only to be revived temporarily by the Obama magic of 2008.

Though Biden has also served as an effective cheerleader in chief (recall his convention speech describing how “night after night, I sat beside [Obama] as he made one gutsy decision after the other”), he is still is regarded as a loose cannon on the stump and bears the brunt of much ridicule in Republican quarters over his gaffes and loquaciousness. Ryan needled him on that Thursday night when Biden mocked Romney’s “47 percent” remarks.

As a veteran of many a debate during six Senate terms and two presidential and now vice presidential bids, Biden has been surprisingly disciplined in such verbal encounters. In his 2008 debate with his Republican counterpart, Sarah Palin, he avoided being overbearing or condescending toward her, a newcomer to the national stage. (Though while taking the fight to Ryan, he may have seemed a bit of both.)

Biden’s political career has seemed on the verge of ending more than once — whether because of the plagiarism allegations that drove him from his first presidential bid in 1987 or his dismal rerun in 2008. But he’s always found a way back.

After he dropped out of the 1988 presidential race, Biden revived his reputation through his leadership of the Senate Judiciary Committee’s confirmation hearings for Supreme Court nominee Robert Bork, which won him laurels from fellow liberals. Later, the controversial hearings that put Clarence Thomas on the highest bench brought him mixed reviews overall but high marks within the party.

Biden never really had a chance in his second bid for the Democratic presidential nomination in 2008, running into the Obama-Hillary Rodham Clinton buzz saw. His occasional gaffes continued to be a drag, seized on by opponents who saw him as easy pickings despite his solid work in the Senate. And in the public eye, his perceived lack of discipline masked his knowledge and experience in domestic and foreign affairs.

His vice presidency may have helped him overcome all that. As Biden approaches his 70th birthday in November, one hears talk — certainly not discouraged by him — of a third presidential try in 2016. At 73, he would be one of the oldest Americans to seek his country’s highest office, surpassing Reagan’s 69 in 1980 and equaling Reagan’s age at reelection.

Much of Biden’s political future, of course, will depend not only on his reelection with Obama next month but also on the administration’s performance — and his own — over the ensuing four years. And then there is the looming specter of Hillary Clinton. Or Mark Warner. Or Martin O’Malley. Or Andrew Cuomo.

Even a reelected Biden would need a substantial improvement in the economy over that time to remain in the speculation about 2016. And his continued subordinate role to a sitting president could pose a problem, as Richard Nixon in 1960, Hubert Humphrey in 1968 and Gore in 2000 all discovered.

Any dramatic closing chapter to the Biden saga would depend as much on Obama as on the man who has been his loyal and active No. 2. For all of Biden’s efforts against Ryan, it remains the president’s job in his debate rematch with Romney on Tuesday night to put their campaign back on track. And, for that matter, to keep alive whatever presidential dreams Biden may yet entertain.

Jules Witcover, a veteran Washington journalist, is the author of “Joe Biden: A Life of Trial and Redemption.”

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