WASHINGTON, Aug. 19 (Xinhua) -- Things are not looking so great for U.S. Democratic presidential candidate Hillary Clinton, who was not long ago seen as the only viable Democratic contender for the White House in 2016 but is now under siege by scandals and opposing candidates.

Indeed, Democratic challenger Senator Bernie Sanders trounced Clinton in recent days in an unofficial poll of attendees of the U.S. state of Iowa State Fair, a testing ground for a slew of candidates who descended on the days-long event in recent days in a bid to gain the attention of media and the U.S. public.

Sanders led Clinton 49 percent to 45 percent in the poll and continued to draw large crowds in recent weeks, as he has tapped into the anti-establishment fervour of the Democratic Party's progressive wing.

Analysts say Clinton must be careful not to underestimate Sanders, and contend that campaign strategists are likely advising her to strike back soon and hard. Indeed, Sanders has been stealing the limelight from Clinton in the past weeks, drawing large crowds and overshadowing her in the media.

He has outshone Clinton on authenticity - a prime draw for many American voters - and has addressed issues such as income inequality, something that appeals to the progressive wing of the Democratic Party.

"Sanders has a set of coherent principles and he seems incredibly genuine about his push for a more progressive political future. His campaign is also literally a bottom up movement which has great appeal," Julian Zelizer, professor of history and public affairs at Princeton University, told Xinhua.

Clinton, in sharp contrast, has always struggled with her public image, often coming across as stiff, out of place among ordinary Americans and inauthentic. Unlike her folksy husband, former President Bill Clinton, Hillary has often stumbled in her attempts to relate to ordinary voters. And even among her supporters, the level of enthusiasm does not match that of Sanders at present, who is riling up large crowds.

"The biggest danger for Clinton is that Sanders wins early on, in Iowa and New Hampshire and generates a kind of momentum that results in a tough primary struggle," Zelizer said. "This can undercut more of the enthusiasm from her overall campaign and expose more weaknesses in the campaign."

Clinton has already underestimated Sanders, Zelizer said, and her supporters did not anticipate the kind of fervor that would emerge behind Sanders' campaign.

Aside from Sanders, there's been some talk of Vice President Joe Biden entering the race to nab the Democratic nomination. While Biden likely presents no major threat to Clinton, he is one more element that can chip away at her nomination bid.

And then there's the email scandal, as the Federal Bureau of Investigation is looking into whether classified information was wrongly handled because she used a private email account and private server while she was secretary of state under President Barack Obama.

Still, Clinton is ahead of every single candidate, both Democrat and Republican, in the latest Real Clear Politics average of head-to-head match-ups.

Clinton now leads Sanders by 47 percent to 29 percent. She also leads Republican frontrunner and billionaire mogul Donald Trump by 6 points, and leads former Florida Governor Jeb Bush, also brother of former President George W. Bush, by 9 points.

And on the bright side for Clinton's team, she has a nationally and internationally recognized brand and will likely get the votes from single women as well as black and Hispanic voters, though recent events have shown that anything can change in this seemingly unusual race to the White House.