Why bother? Many 2016 candidates polling at 1 percent or below -- but refuse to bow out
Republican Senator Lindsey Graham, pictured here in Washington, DC on March 12, 2015, has accused Obama of softening America's power in the Middle East (AFP Photo/Mandel Ngan)

Their campaigns flatlined long ago. But several low-polling candidates in the US presidential race insist they are still viable contenders, even as voters and experts ask: Why?

Jim Webb, for instance, has made zero impact on the race. He exited the Democratic nomination battle on Tuesday much like he entered it -- with few people noticing.

But instead of riding his political horse into the sunset, the gruff-talking former senator and US Marine is threatening one final mission: an independent run against the likes of Hillary Clinton and Donald Trump, respectively the Democratic and Republican frontrunners.

Senator Lindsey Graham keeps spinning his wheels at the back of the broad Republican field, caught between debate-shaping foreign policy guru and political laughing stock with little support.

No support, in some cases. In an August poll of 957 voters in North Carolina, which borders Graham's home state, not one respondent backed him. He fares little better today.

Yet the no-hopers persist, toiling away in a brutal ground game that rewards deep pockets and name recognition.

They smile through gritted teeth, insisting their campaigns are one debate away from catching fire. They wonder whether the candidacies of Clinton, Trump, Jeb Bush or Bernie Sanders will implode, and mercifully send support their way.

But the question observers ask 13 months before the election is, why not pull the plug on campaigns that are clearly on life support?

The arduous, exhausting run for the US presidency is the natural next step for some politicians in the public spotlight, clouded by ego and fuelled by ambition. Dropping out early is not an option.

For others, a longshot 2016 race strategically positions them for a viable vice presidential nod, or lays the groundwork for 2020 or beyond.

Several back-of-the-pack Republicans are stubbornly holding firm, including Graham, Louisiana Governor Bobby Jindal, ex-New York governor George Pataki, and ex-senator Rick Santorum.

None surpasses the one percent bar in the RealClearPolitics poll average.

Democrats in the same bind include former Maryland governor Martin O'Malley and Rhode Island's ex-governor Lincoln Chafee, whose performance at last week's Democratic debate was so awkward that his state's political chorus rose up in unity urging him to quit the race.

"Chafee's good day for dropping out is about a week old now," political science professor Joseph Cammarano of Rhode Island's Providence College told AFP.

Chafee has raised virtually no campaign money. But for many, like Chafee who comes from a politically successful family, "to drop out of the race is to admit failure," Cammarano said.

"It's acknowledging that they're not good enough to win, and that's too hard for a lot of politicians."

- 'Stay politically relevant' -

Chafee said Monday he will remain in the race largely as a reminder that America's rush to war must be constantly challenged, a counterweight of sorts to former secretary of state Clinton, who has endured criticism for her 2002 Senate vote supporting the Iraq war.

Graham relentlessly demands a more muscular US foreign policy, while Santorum sees himself as the moral conservative tilting the Republican field more towards his social and religious agenda.

"They're pushing for something larger than themselves," not necessarily self-validation, Cammarano said.

Two low-polling candidates, Republican Jindal and Democrat O'Malley, appear to be taking more calculated, strategic moves. Both are young and eyeing their political future, sticking with an unwinnable race in the hopes of making gains down the road.

"These guys aren't dumb. They know that they don't want to fail again, so they'll go to school on their mistakes and improve the next time around," Cammarano said.

Jindal has a particular goal in mind: "He's trying to stay politically relevant" while he pursues either the vice presidency this year, or the White House later, said professor Joshua Stockley of the University of Louisiana at Monroe.

As for political animals like Jindal, New Jersey Governor Chris Christie who is also polling poorly, and two-time presidential hopeful Mike Huckabee, "they can not fathom a life of not being a relevant part of the system," Stockley said.

But a presidential campaign is not for the faint of heart, and "we should respect them for persevering, however remote the odds should be," he argued.

Republicans no doubt draw inspiration from Santorum's inspirational 2012 campaign. He was floundering, but traveled by pickup truck to all 99 counties in early-voting Iowa.

His grass-roots effort paid off, and he won the Iowa Caucuses. Santorum eventually lost to Republican nominee Mitt Romney, but his bid was an eye-opener to fellow low-pollers.

"It's part of the narrative of the underdog," Stockley said, "and we all love to root for the underdog."