The question was being asked in hallway whispers and excited chatter in many languages this week at the Clinton Global Initiative conference. It's the question that follows Hillary Clinton everywhere - will she run for US president in 2016?

A version of the question came up during a panel discussion on investing in the future of women, and Clinton was deft, saying only that "someday, I hope" to see a woman president. She stopped short of discussing her own plans, even as applause erupted.

For the former secretary of state, New York senator, and first lady, the four-day meeting at a Manhattan hotel is the latest stop in what many see as an increasingly intense shadow campaign.

Clinton, who has kept busy traveling the country discussing healthcare, voting rights and other policy issues, has acknowledged that she is considering running for president, most recently in a New York Magazine interview published online on Sunday.

But Clinton, who lost the 2008 Democratic presidential nomination to Barack Obama, has not declared definitive interest in a race that would finish when she is 69 years old.

Still, a movement has taken hold around her.

Ready For Hillary PAC is the most organised and best financed of Clinton's independent supporter groups, with a roster of former Obama campaign officials and major Democratic fundraisers. The PAC boasted 10,000 donors and had raised $1.25 million as of August.

Twenty contributors were "bundlers" for Obama in 2012, meaning they donated up to the legal individual limit and then collected additional money from others.

Jeremy Bird and Mitch Stewart, prominent veterans of the Obama campaign's field operation, have signed onto the political action committee.

Philadelphia lawyer Daniel Berger, an Obama campaign bundler and early Ready for Hillary donor, said he was asked to contribute because of his support for the party.

"It wasn't at her request. I haven't spoken to Hillary in years, since 2008," he said, adding that he is close to her husband, former Democratic President Bill Clinton.

Berger noted that neither Clinton has any connection to the PAC.

Long-time Democratic donor Peter Buttenwieser, a Philadelphia philanthropist and Obama backer, also gave to Ready For Hillary so that he would be on the record supporting her.

"It's a very natural sort of move to the 2016 presidential election and in that election I feel that, hands-down, Hillary Clinton is the most qualified and important candidate in the Democratic Party," he said.

High-profile Democratic officials also have encouraged Clinton to run, including Senators Kirsten Gillibrand of New York and Claire McCaskill of Missouri. Former Michigan governor Jennifer Granholm also has backed the PAC.

Ex-Clinton staffers and allies also are tied to Priorities USA Action, a super PAC that supported Obama in 2012 but has not officially announced plans for future elections.

All this means that should Clinton run, a formidable team would be already mobilised and tapped into her donor base.

Preliminary polling numbers support speculation that Clinton will run. She leads a potential Democratic field by 40 per cent in the most recent Reuters/Ipsos tracking poll, carrying 51 per cent of voters, compared with 11 per cent for Vice President Joe Biden, the runner-up.

Clinton's presumptive front-runner status is not limited to the Democratic field. Her closest national matchup in the poll comes against New Jersey's Republican governor Chris Christie, who pulls in 25 percent of the vote to Clinton's 44 percent.

RETURNING TO THE POLITICAL STAGE

Clinton's re-emergence gained momentum this fall with the rebranding of her family's Clinton Foundation - now called the Bill, Hillary, and Chelsea Clinton Foundation.

Around that time, she signed a deal with publisher Simon and Schuster to write a book about her time as secretary of state, due out in 2014.

The Obama administration took advantage of her September 9 appearance at the White House by allowing her to speak about the Syrian crisis at a time when Obama was seeking congressional and public support.

On Tuesday, Clinton again ventured into politics, talking about healthcare policy ahead of a threatened government shutdown that could come next week as some Republicans in Congress refuse to negotiate without defunding Obama's healthcare law.

She also introduced Obama and Bill Clinton as they spoke about healthcare Tuesday.

After keeping a relatively low profile soon after her February departure from the State Department, Clinton stepped back into the fray with public remarks about gay marriage and voting rights. Her words carried potential appeal for the party's progressive wing, which sided with then-Senator Obama in her 2008 race against him.

Some of Clinton's paid speeches, which command hundreds of thousands of dollars, have focused on another potentially important group: Wall Street. She spoke to private equity giants Carlyle Group and Kohlberg Kravis Roberts during the summer, according to reports.

The groundswell of support for Clinton also has eclipsed concerns about her health that arose in late 2012 when she was hospitalised for a blood clot in her head.

Clinton's work with the family foundation has kept her ties to major donors active, as her family has hosted and planned fundraisers for the group in Washington, San Francisco, London, and New York's tony Bridgehampton. She also has helped raise money for Terry McAuliffe, a close friend running in a tight race for governor of Virginia.

Her refusal to talk about a presidential bid has not stopped supporters from speculating and giving money to a campaign that may not happen.

"The PAC was not created at her insistence or as a result of her efforts," Berger said. "But Hillary has spent many years in public life, both in an official and unofficial capacity. And it seems not only possible, but probable, she will run for president in 2016." - Reuters