For a candidate with such a commanding lead in the polls, Hillary Clinton has a staggering amount riding on the upcoming Democratic presidential debate.
She began the campaign with every possible advantage – universal name recognition, popular support from her time as secretary of state, a mighty political machine, near universal support of the Democratic Party's establishment and a mountain of money.
But after a long summer of relentless Republican attacks over her use of a private email server while serving as Obama's chief diplomat, the deaths of four Americans in Benghazi during that time and a surprisingly effective assault from the left by Vermont senator Bernie Sanders, she has seen her favourability plunge from the mid-60s to the low 40s.
Though most Democrats accept that the attacks on her over the email system and the Benghazi attack appear to be politically motivated – indeed a Republican leading the Benghazi investigation clumsily admitted so earlier this month – they have been shocked at how poorly Clinton has performed in her own defence.
Indeed it is this failing on her own behalf that has led to some Obama operatives – who are terrified she might lose an election to Republicans that will dismantle his legacy – to begin the push for a run by Vice President Joe Biden.
Clinton will use the debate to try to convince her party she is up to the job not only of connecting with and exciting Democratic voters, but taking on and defeating the eventual Republican candidate.
For all that, few observers believe the event will be as combative as the two Republican debates that have preceded it.
Clinton's main adversary on the state in Las Vegas will be the gruff socialist Senator from Vermont, Bernie Sanders, who has insisted he is not interested in personal attacks.
With this no-nonsense approach Sanders has already managed to drive his support from around 8 per cent in June to 25 per cent now. He has a reputation for honesty and integrity that he is unlikely to surrender with attacks on Clinton in the debate.
And Clinton cannot afford to offend Sanders' supporters, who she one day hopes to win over herself.
Also on the stage will be three long-shot candidates, Jim Webb, Martin O'Malley and Lincoln Chafee, all three of whom have barely registered in the public eye since their campaigns began. Simply appearing on stage alongside Clinton and Sanders will be a victory for them.
Who's who
Hillary Clinton
A former secretary of state, senator and first lady, Clinton's qualifications are utterly unimpeachable.
But her retail political skills have always let her down. She was expected to easily win her party's nomination in 2008 before a little-known senator called Barack Obama snatched the prize from her.
Despite the challenge being mounted by Sanders this time around, most people think she will still win the nomination. But some fear she could be dangerously diminished by the race. Clinton's evasive and changing answers to the email questions have demolished her personal standing, with most Americans now viewing her as untrustworthy and unsympathetic.
Clinton has fallen into second place in Iowa and New Hampshire, with reports that some in her campaign think she should abandon New Hampshire entirely.
Clinton's strength is her relationship with minority voters, particularly African-Americans, who have fond memories of her husband's presidency in the 1990s. Iowa and New Hampshire are two of the whitest states in the union, but beyond that are Nevada, where the Hispanic vote will be telling, and South Carolina, where the Democratic party is almost completely dominated by African-Americans.
While she originally planned to cite her centrist credentials and electability during the primary season, Clinton has moved sharply to the left on a number of issues, vowing action on gun control, climate change and abandoning her previous support for free trade to oppose the Trans-Pacific Partnership. Clinton's campaign has shifted from hoping for a quick primary victory into a strategy of grinding out victory by relying on the votes of blacks, Latinos and working class whites. She remains the heavy favourite and the consensus candidate of the party establishment, particularly if the Vice President does not run. Clinton currently is at 42 per cent in the RealClearPolitics compilation of major polls.
Bernie Sanders
The 74-year-old socialist has been an independent member of Congress for almost 25 years and a senator from Vermont since 2007. An outspoken advocate for civil rights, universal healthcare and action to combat climate change, Sanders rose to national prominence with a 2010 marathon denunciation on the floor of the Senate against tax cuts for the wealthy.
With a stooped back, shock of white hair and the gruff demeanour of a prickly university professor, Sanders was originally given little chance when he announced his campaign for the Democratic presidential nomination back in April. However, buoyed by growing liberal disenchantment with Clinton and his own reputation for no-nonsense straight talk, Sanders has surpassed the former secretary of state in the polls in both Iowa and New Hampshire and has narrowed the gap considerably in national polls.
A determined campaigner against the influence of money in politics, Sanders has shrugged off the hostility of Wall Street Democrats and instead copied the early example of Barack Obama in 2008 by raising enormous sums of money in small amounts by tapping a vast donor network of ordinary, middle class Americans.
Sanders has rejected attack ads, vowing to campaign strictly on the issues and any direct assaults on Sanders by Clinton are likely to backfire badly among a Democratic electorate that views Sanders very favourably.
Sanders' biggest weakness may be his long-standing support for the rights of gun owners, an unpopular position with the Democratic faithful that Sanders now appears to be abandoning. The Vermont Senator is a non-observant Jew, though he has become fond of quoting Pope Francis. Sanders is currently at 25.4 per cent in the RealClearPolitics compilation of major polls.
Jim Webb
Webb has been an award-winning journalist, is an author of 10 books and taught at Harvard and the US Naval Academy. A former Republican, Webb is also a highly decorated Vietnam War veteran and served as Secretary of the Navy under President Ronald Reagan. However, Webb was an early and prominent critic of the Iraq War, calling it "the greatest strategic blunder in modern memory" and turned against the GOP. He waged a long-shot campaign for the Senate in Virginia in 2006 and shocked the American political establishment by defeating the incumbent Republican.
He had a moment of fame in November 2006 when refused to stand in line with other newly-elected senators to have his photo taken with President Bush. When Bush approached Webb and asked about his son, who was serving in Iraq, Webb replied that he wanted to get his son out of Iraq.
During his six years in the Senate – he did not seek re-election in 2012 – Webb focused on veterans affairs, opposing the Iraq War and reforming America's policies of mass incarceration. Webb is currently at 0.9 per cent in the RealClearPolitics compilation of major polls.
Martin O'Malley
The former mayor of Baltimore and two-term governor of Maryland, O'Malley is waging a long shot campaign for the nomination. O'Malley was hoping to be the left-wing alternative to Clinton until Sanders occupied that space for himself.
As governor O'Malley carefully established his liberal credentials by backing offshore wind farms and backing gay marriage.
But – to the extent that it has been noticed at all – his campaign has been bruised by his record as mayor of Baltimore, where his tough-on-crime policies are seen by some to have contributed to the conditions that lead to the devastating riots earlier this year.
O'Malley is currently at 0.6 per cent in the RealClearPolitics compilation of major polls.
Lincoln Chafee
Another former Republican, Chafee is a Yankee blueblood whose father was US Secretary of the Navy in the 1960s, governor of Rhode Island and Senator from Rhode Island from 1976 to 1999.
Chafee succeeded his father in the Senate as a Republican, but soon found himself at odds with the new right-wing administration of President George W. Bush. In 2004 Chafee refused to support Bush for president, instead writing in the name of Bush's father, who served as president from 1989-1993. In 2006, Chafee ran for re-election, but with Rhode Island a very liberal state and the country in the grip of a ferocious reaction against the Bush administration, Chafee was defeated by a Democrat and lost his Senate seat. In 2007, out of office, Chafee abandoned the Republican party to become an independent and soon endorsed Barack Obama for president.
In 2010, Chafee ran for governor of Rhode Island and won. In 2012 Chafee was a co-chair of Obama's re-election campaign and in 2013 he announced he was dropping his independent status to formally join the Democratic party.
Chafee declined to run for re-election as governor in 2014, instead declaring his intention to run for president as a Democrat. Chafee is pro-choice and pro-gay rights, opposes tax cuts for the wealthy, favours gun control, and action to combat climate change. In 2002 Chafee was the only Republican in the Senate to vote against the Iraq War. Chafee is currently at 0.2 per cent in the RealClearPolitics compilation of major polls.
Joseph Biden
The vice president, Joe Biden, is the wild card in the coming primaries. He is not appearing in the debate but is known to be considering making a run.
It is understood Biden, who will be 73 in November, is being encouraged by Obama supporters who are concerned that Clinton has so far failed to either connect with the Democratic base or adequately explain to voters why she broke regulations to use a personal email server as secretary of state.
Biden is Clinton's political antithesis, warm where she is cold, happy on the stump and prone the sort of gaffes people willing to speak off-the-cuff make.
Biden is no stranger to presidential politics, having run unsuccessfully for the White House in 1988 and 2008. A long time member of the Senate Foreign Relations Committee, Biden opposed the Persian Gulf War in 1991, but voted to authorise force against Iraq in 2002.
However, Biden soon became a critic of the Iraq War and opposed President Bush's troop surge into the country in 2007.
Long one of the most resolutely middle class of all US Senators, Biden was known for taking the train home to his family in Delaware during breaks from his Senate duties. Biden lost a wife and infant daughter in a car accident in 1972 and then lost his 46-year-old son Beau to brain cancer in May this year.
A stout liberal, Biden came out in support of gay marriage before Obama did and is an environmentalist, opposing oil drilling in the Alaskan wildlife refuge and supporting action to combat climate change. While in the Senate Biden co-sponsored the Global Warming Pollution Reduction Act with Bernie Sanders, the most stringent climate change bill in the Senate. Biden is a friend of organised labour, though he has been mostly supportive of free trade and if he does run, he might be the only Democrat pursuing the nomination to support the TPP.
It is widely believed Biden must make his intentions known within the next few days. Although CNN invited Biden to participate in the debate, he has not accepted. While it is uncertain how a Biden candidacy would affect the race, most observers believe he would pull the bulk of his support from Hillary Clinton, the other member of the political establishment running. Biden is currently in third place in the RealClearPolitics compilation of major polls, with 18.6 per cent.
