By Laura Smith-Spark
BBC News, Washington
Barack Obama may have overtaken Hillary Clinton in the fundraising stakes, but the New York senator has a trick up her sleeve which she is unveiling on the presidential election campaign trail this week - husband Bill Clinton.
Will Bill Clinton's public presence remind voters of past scandals?
Mr Clinton's abilities as a speaker are undoubted - and he has already been putting them to use at big-money fundraising events on his wife's behalf.
He also enjoys the respect verging on reverence that many Americans accord their former president.
But on the other side of the coin, his very charisma brings with it the danger that he will overshadow Hillary and highlight what critics say is her lack of warmth.
Mr Clinton's reappearance on the campaign trail also risks reminding Americans of the Monica Lewinsky sex scandal and his subsequent impeachment - giving ammunition to his wife's opponents.
So what does Mrs Clinton stand to gain by campaigning with Bill by her side at rallies in Iowa and New Hampshire in the coming days?
Appeal to the base
According to pollster John Zogby, Mrs Clinton will find Bill Clinton's popularity with the Democratic core a major asset as she strives to win her party's nomination to run for president in 2008.
Mrs Clinton needs to get clear of her closest rivals
Mr Zogby says: "She has carved out a position for herself in the centre, which is a general election strategy.
"However, she still has to win the primaries... and Bill Clinton helps her to drive and shore up the base of the Democrats."
Mr Zogby points out that Bill Clinton left the presidency in early 2001 with very high approval ratings "despite everything" and continues to be popular with many Democrats, if not Republicans.
"There are still residual feelings [of hostility] about Bill Clinton - but they are first and foremost from the people who hate both of them and aren't going to vote for her anyway," Mr Zogby says.
The publication last month of two books about Mrs Clinton also caused less of a stir than she perhaps feared, with no major new revelations about her sometimes turbulent marriage.
Putting Mr Clinton on the same stage as Mrs Clinton, even in front of supporters, does however pose certain challenges for her campaign team.
Commentators point to the ex-president's powerful eulogy last year at the funeral of Coretta Scott King, widow of Martin Luther King, as an example of his capacity unintentionally to outshine his wife.
The Clintons acted out a campaign video spoofing The Sopranos
"When Bill and Hillary come into the room, if Bill isn't careful he sucks all the political oxygen out of the room and takes it away from Hillary - and for her that's a liability," Dr James Thurber of American University told the BBC.
"So they are going to have to play that very carefully, keep him apart to a great extent, use him for campaign finance behind the scenes - and boy, is he good at that."
Campaign spokesman Howard Wolfson, in a message to supporters, has given a clue as to what Bill Clinton's carefully-managed role on the campaign trail will be.
"As Hillary lays out her vision on the stump, he will be invaluable in filling in the details about her life, her background and her accomplishments for Americans to get to know her better," Mr Wolfson said.
Observers say Mr Clinton's emphasis on his wife's personal history is intended to make her more "human", countering a perception among some voters that she is cold and ambitious.
The Clintons' recent joint appearance in a video parodying the final episode of US TV drama The Sopranos has been seen as a similar attempt to cast Hillary in a warmer light.
The fact that Bill Clinton is joining the campaign in Iowa and New Hampshire is also no coincidence, analysts say.
Both states are among the first to choose their candidates - giving them greater sway over the process - and both retain a fondness for Mr Clinton, says New Hampshire political analyst Dean Spiliotes.
Outrage over Bill Clinton's affair with Monica Lewinsky has faded
Iowa is also the state where Mrs Clinton has trailed Mr Obama and Mr Edwards in some polls, despite holding a lead in national surveys.
Mr Spiliotes believes the passage of time has been the biggest factor in rehabilitating Mr Clinton as a political asset.
Back in 2000, Mr Clinton was used "very carefully" in campaigning for Al Gore, his vice-president who narrowly lost out to George W Bush in the race for the presidency.
"They thought that he was radioactive in certain parts of the country because a lot of the Monica Lewinsky stuff was still very alive in people's minds," says Mr Spiliotes.
"To some extent that has changed. He has become a very popular ex-president with a broad cross-section of society."
'People love Bill'
Pundits' predictions of Bill Clinton's largely positive impact are borne out by speaking to likely Democratic and Republican voters in New York, the state Mrs Clinton represents in the Senate.
Democrat Kristen Knight loves Bill Clinton but is less keen on Hillary
Kristen Knight, a 26-year-old graduate student and Democratic supporter, says: "People love Bill - I love Bill. Democrats especially have a rosy glow when they think about him.
"Whether or not he will help Hillary I don't know, because she's very polarising. But probably he will help because people like to be around him."
Republican supporter Jay Buth says: "The American public has a fairly short memory. His appeal to the mass audience out there will be a positive for them, not a handicap."
PJ Jumonville, a 34-year-old Democratic supporter, agrees: "I don't think his scandals will make that much difference, the public doesn't really worry about them. Peccadilloes are not the same thing as going to war."
But as retired bookseller Mary Butler, a Democrat, points out, whether voters in America's heartlands will be as forgiving as traditionally more liberal New Yorkers remains to be seen.
"His past scandals are nothing compared to what is going on now, unless you think sex is the only thing that counts," she says. "But what the people in Iowa think about him I don't know."
One thing is certain: Bill Clinton's appearances by Hillary's side are sure to draw many eyes, and that will give him an unrivalled chance to be her best advocate.
In his words: "The only reason to elect a president is that the person running would be the best president - and you will never find anybody who will do a better job than she will."