Former vice president Joe Biden asked a town hall audience in Hanover, New Hampshire on Friday: "Imagine if, God forbid, Barack Obama had been assassinated after becoming the de facto nominee. What would have happened in America?''. Watch the video above.

Democratic presidential field shrinks as debate cut looms

The 2020 presidential election is still more than 14 months away, but with an early key deadline looming this week, the record field of Democratic hopefuls is dwindling.

With a trio of 70-somethings breaking away from the pack - Biden, independent Senator Bernie Sanders and fellow progressive Elizabeth Warren - four of the cash-strapped, younger or lesser-known candidates have so far thrown in the towel.

Others are likely to bow out in the coming days, as the list of those qualifying for the party's third round of debates is to be revealed on Thursday.

Only 10 of the remaining 21 candidates have met the qualifying criteria -- based on poll numbers and fundraising success -- and most of those are still struggling to catch up with the Big Three.

Even two high-profile candidates from New York state -- New York Mayor Bill de Blasio and Senator Kirsten Gillibrand -- may fail to reach the debate stage, effectively leaving their candidacies in limbo.

Biden has managed to maintain a significant lead despite a rocky summer marred by a proclivity for gaffes -- which some have called a worrying trend given the months and months of campaigning ahead.

The Democratic primary season really only starts in earnest with the Iowa caucuses in February -- and some analysts question whether the 76-year-old Biden might lack the fire or the endurance needed to stay on top.

That has kept hope alive for second-tier candidates, but that sense of optimism could fade if they miss a chance to go toe-to-toe with their rivals on national television on September 12 in Houston, Texas.

The debate offers an opportunity to both make a direct pitch to American voters -- and attract all-important donors

"Without access to a debate audience, some candidates have realised that their bids are hopeless," said Kyle Kondik of the University of Virginia Center for Politics.

"I suspect more will come to this conclusion soon."

Making the cut

Leading the pack so far is Biden (at 29 percent in a RealClearPolitics average of recent polls), followed by Sanders (16 percent), Warren (15 percent), Senator Kamala Harris (seven percent) and Pete Buttigieg, the mayor of South Bend, Indiana (five percent).

Also securing spots in the debate are former Texas congressman Beto O'Rourke, Senator Cory Booker, businessman Andrew Yang, former Obama-era cabinet member Julian Castro and Senator Amy Klobuchar.

If any other candidates make the cut before Thursday, the group might be split in half and a second debate will be added on September 13.

Of course, failing to make the debate stage is not necessarily a death knell for a candidacy -- but it certainly doesn't help.

Some candidates who fall short of qualifying will likely decide to battle through regardless, at least until Iowa, said Christopher Arterton, a professor of political science at George Washington University.

"There's kind of an ever-hopeful quality to presidential candidates," Arterton told AFP.

Democrats are quick to point to the experiences of Jimmy Carter and Barack Obama, two men who defied the oddsmakers and the political pundits by pulling off surprise victories in Iowa before going on to win the White House.

'Swallow a bit'

Biden -- Obama's vice president for eight years and a senator before that for decades -- has not yet been seriously challenged in the race despite the gaffes, fears about his age, the increasingly frontal attacks of his rivals and Donald Trump's cutting gibes.

For many Democrats, the absolute requirement of any candidate is the ostensible ability to defeat Trump in November 2020.

Biden's campaign team itself, including his popular wife Jill, makes this argument.

"Your candidate might be better on, I don't know, health care, than Joe is but you've got to look at who's going to win this election and maybe you have to swallow a little bit ... but your bottom line has to be that we have to beat Trump," she told a group of Democratic voters.

Biden's lead -- due in part to strong support from blue-collar workers and African-Americans -- has been surprisingly steady.

But Atherton, for one, doubts that will last.

"I happen to think that Joe Biden's campaign is going to collapse once we actually get into primary voting," he said.

That could leave an opening for the 70-year-old Warren, an outspoken critic of Wall Street and corporate America who has been steadily rising in the polls.

Following her solid performances in the first two debates and bolstered by a detailed set of policy proposals ("I've got a plan for that" is one of her favorite lines), she has surged past Sanders in several polls.

Warren "may be consolidating the liberal support behind her," said Mitchell McKinney, a political communications specialist at the University of Missouri.

"If she pulls out Iowa, then we have a new frontrunner."