Why outgoing presidents stay off the campaign trail

It's easy to see how much a large, adoring crowd energizes President Obama outside of Washington, yet the 44th president indicated Sunday that he may not be spend much time campaigning for his potential successor in 2016.

"I think the American people, you know, they're going to want that new car smell," he told ABC News. "They want to drive something off the lot that...doesn't have as much mileage as me."

The American people are "probably not gonna be looking at me to campaign too much," he concluded.

He's hardly the first president to consider whether staying away is the best way he to help his party hang on to the White House. The act of governing often brings down presidential approval ratings, which can make the outgoing occupant of the Oval Office something of a dead weight.

At first glance, this might seem to be the case, but if you look at the last few two-term presidents, it's not always that simple.

Former President George W. Bush, like President Obama, was suffering from approval ratings that were already hovering in the low 30 percent range when the election got underway in 2007, and by 2008 they had sunk even further to a range of the mid 20- to low 30-percent range.

He did just one public event for 2008 Republican nominee John McCain: a Rose Garden endorsement after McCain clinched the GOP nomination, according to the count kept by CBS News White House Correspondent Mark Knoller. And of four fundraisers Mr. Bush did for McCain's campaign, McCain appeared at just one - -and that was closed to the press.

Mr. Bush didn't even address the GOP convention in Minnesota that year, instead giving his speech before the TV networks even began broadcasting their live coverage of the event.

But McCain also harbored some bad feeling toward Mr. Bush, after a bitter nomination fight against him in 2000. Still, Bush wrote in his 2010 book, "Decision Points," that he would have liked to have campaigned for McCain. "I was confident I could have helped him make his case. But the decision was his. I was disappointed I couldn't do more to help him," he wrote. And Bush "understood he had to establish his independence."

For Al Gore, the Monica Lewinsky scandal was the obvious taint that made him want to put as much mileage between his presidential campaign and Bill Clinton. Although Clinton did not suffer a major decline in his job approval ratings -- they stayed in the 55 to 65 percent range during 1998 -- Gore still steered clear of his boss once he was campaigning.

Gore, who had stood by Clinton during the scandal, made only a brief reference to him when he declared his candidacy and soon after called the Lewinsky affair "inexcusable" and "terribly wrong" in an interview with ABC News.

The two men appeared together at the 2000 Democratic National Convention, but Gore's advisers reportedly declined the White House's offer to make Clinton more of a fixture on the campaign trail during the election. Gore's advisers always insisted he needed to win on his own terms.

Eventually, Clinton's image was rehabilitated by his political talent on the stump: after his wife lost her bid for the nomination in 2008 and joined the Obama administration, Clinton was a key surrogate for Mr. Obama during the 2012 election, appearing in a documentary style video the campaign created and paid advertisements, showing up with Mr. Obama at two rallies and holding countless others across the country to get Democrats fired up. He was also given a prime speaking role at the Democratic convention that year and gave such a well-received speech that it even won praise from Mr. Obama's opponent, Republican nominee Mitt Romney.

Ronald Reagan differs from the other presidents here, in that although his popularity had suffered after the Iran-Contra scandal became public in 1986, by 1988, his approvals were up in the mid-50's, certainly good enough for his vice president, George H.W. Bush to run a campaign that mostly promised to be a continuation of the Reagan presidency. Reagan didn't do much to promote Bush, tacking an endorsement onto the end of a fundraising speech, according to news reports at the time, but Bush still triumphed. And as the University of Virginia's Miller Center points out, that victory gave Bush the distinction of being the only vice president to be elected directly to the presidency from the vice presidency since Martin Van Buren.

Mr. Obama's approval ratings have been hovering in the low 40-percent range for most of his second term, and most of the endangered Democratic Senate incumbents fled his company during the midterm elections (and most of them lost, anyway). Hillary Clinton, the likely front runner if she jumps in the Democratic primary, has already showed a willingness to seek some distance from the president on issues like foreign policy even though she was his secretary of state. If her past run for the presidency is any guide, she's more likely to try to remind voters of their fond memories of her husband's presidency.

It is always a little awkward for the nominee to get out from under the shadow of the president of his or her party, but it may be less the case if the president seems not to have worn so well on the public in the last couple of years of his presidency.

And if you ask Mr. Obama, he's fine with that.

"You know, one of the benefits of running for president is you can stake out your own positions...and have a clean slate. A fresh start," he said.