Hillary Clinton likes to tell voters what she’s not doing: running for President Obama’s third term.

That’s to downplay what she is doing: asking voters to pick a Democrat to occupy the Oval Office for 12 consecutive years.

Americans have agreed to do that just once in the past 179 years, and those unprecedented reelections of Franklin D. Roosevelt, the last as World War II neared its end, helped spark a constitutional amendment on term limits. The last nominee to win a third consecutive term for their party was Republican George H.W. Bush in 1988.

But one of her biggest long-term challenges will be convincing a fickle electorate that her presidency would represent something different than the past eight years — while still warmly embracing Obama’s legacy to keep enthusiasm high among the president’s core supporters who propelled him twice to White House victories.

“Democrats should not only defend this record and protect this record, they should run on the record,” Vice President Biden said in announcing last month that he would not be the one to do so.

Whether or not that strategy is followed, Clinton will be challenged to pull off what Al Gore couldn’t in 2000 and John McCain couldn’t in 2008.

“She has a lot of fancy footwork to do,’’ said Douglas Brinkley, a presidential historian at Rice University. “People typically get fatigue over one party and decide to give another party a try.’’ With Republicans taking aim at Obama’s policy in the Middle East in the aftermath of the Paris terror attacks, foreign policy could become particularly challenging for Clinton, Obama’s former secretary of State who’s long favored a more muscular approach in Syria.

Here’s what may determine if she’ll succeed:

History and demographics

Of course, there are many reasons why history may be a bad guide for 2016. Clinton would be the first female nominee of either major party. As the wife of a former president and the nation’s former top diplomat, she is also one of the most well-defined candidates in presidential history.

There are also major demographic shifts. In the last six elections, Republicans have won the popular vote just once, in 2004, as voter concerns about national security and the war in Iraq were tantamount. Since then, about six more percentage points of the white vote has disappeared, according to Census figures.

“They can’t win with George Bush’s coalition in 2016,’’ said says Joe Trippi, a Democratic strategist who was former Vermont governor Howard Dean’s campaign manager in 2004.

“All the arguments about ‘well no one’s ever done it … all those things happened in a world that was literally a 90% white vote.’’

Approval ratings

Approval ratings of Clinton and Obama — specifically their peaks and valleys — have closely tracked for much of the past two years, according to an analysis from FiveThirtyEight. Though Clinton’s numbers remained higher than Obama’s throughout, the two have converged since she announced her candidacy.

That’s not necessarily a good thing.

An August Monmouth University poll found just 27% of registered voters would vote for Obama for a third term if he could run for one; among Democrats, 43% want someone else.

“Obama is exerting a significant drag on her,’’ said Larry Jacobs, a presidential politics expert at the University of Minnesota.

“That helps to explain why she’s trailing most of the Republican candidates,’’ he said.

The Obama economy

Of all the issues, the economy will prove the most vexing for the 2016 candidates, and especially so for Clinton.

Obama is credited with bringing the nation out of the most severe financial and economic crisis since the Great Depression, and the latest jobless rate has dipped to 5%. Still, Americans are very pessimistic about the future and wages remain stubbornly stagnant.

According to a recent NBC/Wall Street Journal poll, just 27% of Americans feel they are getting ahead financially. Sixty-four percent say the country’s on the wrong track.

“She’s got to be careful not to overpraise Obama’s economic record but talk about building on it,’’ said Brinkley. Democrats have long reminded voters that they inherited an economic crisis. But it’ll be harder to blame Bush, who left office eight years ago, for it in this election.

The black vote

Both of Obama’s elections relied heavily on unprecedented African-American turnout.

With white working-class voters on the march to the Republican Party, Clinton will be hard pressed to recapture her party’s previous levels of support from this critical demographic. That means she needs African Americans, and possibly even as much as Obama did.

“If she starts trying to dilute the Obama presidency or reject programs like his historic trade pact, Obama could campaign for her but say ‘I’m not going to the mat for her,’’’ said Brinkley.

“To bring out the African American vote Barack Obama almost has to go on a frenzied campaign. Being lukewarm won’t do the trick.’’

Republicans already have their talking points

Clinton’s approach could be irrelevant.

Republicans have made clear they’ll link her to Obama every chance they get, particularly on Obamacare, given her record as first lady of trying, and failing, to pass a broad health-care overhaul.

And given her status as Obama’s first-term secretary of State, they’ll also emphasize criticism of the president’s policies toward Russia, Libya and Syria. “Hillary Clinton has a Barack Obama problem,’’ says a memo written last year by the Republican outside group America Rising PAC.

Clinton is already showing how she plans to talk about Obama.

In her stump speech, she says she wants to build on Obama’s successes, including Obamacare, by expanding its focus to prescription drug costs.

In Saturday’s second Democratic debate in Des Moines, Clinton said “I think President Obama deserves more credit than he gets for what he’s gotten done in Washington despite the Republican oppression,” repeating an applause line she often gives on the campaign trail.

At a South Carolina forum last week, she also said  “I want to build on the progress he’s made, but I want to go further.”

She’s also put some distance between herself and a few of his policies. She recently said she opposes the Trans-Pacific Partnership trade pact, and she supports a no-fly zone over parts of Syria. If Clinton wins the nomination, she’ll face increasing pressure to outline how she’d differ from Obama in her approach to the Middle East.

At the South Carolina  forum, Clinton saluted the president she hopes to succeed, but sought to present herself as having a different charter.

Obama’s “principle challenge was saving us from the terrible financial crisis he inherited,’’ Clinton said. “For me this is about how do we have a New Deal. How do we give everybody new chances?”

Follow @HeidiPrzybyla on Twitter

Read or Share this story: http://usat.ly/1NUqg9j