The race for the White House has seen an unpredicted swing in the crowded field of presidential hopefuls - the rise of the no-hopers, who, for now, seem to pose a threat to the Democratic and Republican front runners.

Two names have come to the fore: Democratic senator Bernie Sanders and property tycoon Donald Trump.

At a rally in Madison, Wisconsin, earlier this month, Senator Sanders drew a crowd of 10,000 people - the biggest of the season. In the key primary state of New Hampshire, one poll shows that he is just under 8 percentage points behind former secretary of state Hillary Clinton.

Surprisingly, Mr Trump, whom many thought was running just for the publicity, is also rising in some polls despite his comments about Mexicans being rapists, which resulted in stores such as Macy's dropping his products and two TV networks dropping shows he is associated with - The Apprentice and the Miss USA pageant.

The latest Economist/YouGov poll, released last Thursday, shows that Mr Trump holds 15 per cent of the Republican vote nationally, overtaking front runner Jeb Bush, the former Florida governor, who has 11 per cent.

A North Carolina poll by Public Policy Polling, released last Wednesday, also shows that Mr Trump is the top choice of Republican primary voters in that state.

Media interest in Mr Trump is so high that he has stolen the limelight from the two most recent Republican candidates to announce their presidential bids - New Jersey Governor Chris Christie, who made his announcement on June 30, and Wisconsin Governor Scott Walker, who entered the race on Monday, bringing the total number of Republican candidates to 15.

Intense press coverage of Mr Trump "puts his name on the top of people's heads", which might explain why he is ahead in some polls, said political science professor David Redlawsk, director of the Eagleton Centre for Public Interest Polling at Rutgers University in New Jersey.

Interest in Mr Trump and Senator Sanders also stems from the fact that they are relative unknowns compared with the "establishment candidates", say experts.

On the Republican side, many conservatives find Mr Bush and Senator Marco Rubio too moderate and are deeply concerned about the "liberalism of American culture", said Associate Professor Jesse Rhodes of the political science department at the University of Massachusetts, Amherst.

By contrast, Mr Trump is a "breath of fresh air" because "he takes very strong and controversial stances on key social issues, such as immigration, and is unapologetic about it", he said.

Similarly, Prof Rhodes said, Senator Sanders is viewed as "more consistently liberal" on key issues such as health care, poverty relief and business regulation.

"Liberal Democrats are hungry for a dyed-in-the-wool progressive candidate, and Sanders is offering them what they want," he said.

When asked about Senator Sanders' ability to draw in the crowds, Mrs Clinton told reporters that "we each run our own campaigns, and I always knew this was going to be competitive".

Already, experts say, while Mrs Clinton is not attempting to engage Senator Sanders head-on, she is moving to the left on issues such as taxation and poverty relief.

In Mr Trump's case, some members of the Republican Party and fellow White House aspirants have come out strongly against him.

For example, Mr Bush called the "rapists" comment "extraordinarily ugly" and unrepresentative of the party.

For now, Senator Sanders and Mr Trump seem to be providing liberals and conservatives with the authenticity they crave.

Mrs Clinton, Mr Bush and Senator Rubio are viewed as "political actors willing to do anything to get nominated", said Prof Rhodes. "From this perspective, the unvarnished approaches of Sanders and Trump are a virtue."

But will they be able to ride the current wave of popularity all the way to the White House?

Prof Redlawsk suggests that those now supporting Senator Sanders may decide later that he is unable to win a general election, while Mr Trump's divisive comments, despite appealing to some segments of the population, "are likely to eventually rebound against him".