US election: Will Hillary Clinton run for President in 2016?

Her aides are however still determined to avenge that defeat and think she would cruise to the nomination.

At 64, she is still young enough and healthy enough to bid for the White House, though her husband Bill has admitted she is "tired" after 20 years of active public service.

The former president has said he has "no idea" if she will make another bid for the White House, but he did more than anyone to spark speculation when he declared her to be the best public servant and campaigner he had encountered.

"She's an extraordinarily able person. I've never met anybody I thought was any better than her at this," he said.

Newt Gingrich, the former Republican Speaker of the House, observed this week that Mr Clinton is "collecting IOUs" by campaigning for President Obama, in case Mrs Clinton wants to bid for the presidency.

"Knowing Bill Clinton, I am confident that he thinks her running in 2016 is a good idea," he told Fox News.

According to the New York Times, the first question some other potential Democratic candidates are asking themselves is whether or not Mrs Clinton will run.

Andrew Cuomo, the governor of New York, reportedly told an adviser: "First, I've got to figure out what Hillary is doing."

The Clinton camp is however adamant that she has not made up her mind about 2016.

Her experience in 2008, when she lost after being the overwhelming favourite, could well put her off, said a former White House official in the Clinton administration.

"You have to understand that if you run for president, unless you are already president or vice-president, the odds of winning are low, no matter who you are," he said.

"She would give up a life of ease, comfort and the freedom to do whatever she wants, and with her approval ratings at an all-time high, to spend two and a half years eating horrible food, staying in horrible hotels and meeting horrible people," he said, referring to the campaign trail.

A Democratic strategist in Washing! ton added: "There is constant gossip about this. But she would return to electoral politics and run the risk of instantaneously become a polarising figure again, whereas now she has an aura of respect from all sides and can go out on a high."

Other considerations will play on Mrs Clinton's mind. If Mr Obama wins, she would have to remember how rare it is for either party to win the presidency for three consecutive terms.

On the other hand if Mitt Romney wins she would be running against an incumbent, who in all likelihood would have presided over an economic recovery.

"The Clintons are very powerful and very ambitious people, and they have always wanted this for her, but this is not a slam dunk," said the strategist.

Follow our US Election coverage as Mitt Romney and Barack Obama fight it out to become President.