WASHINGTON, Sept. 10 (Xinhua) -- Vermont Senator Bernie Sanders has outperformed Democratic presidential front-runner Hillary Clinton for the first time in the U.S. state of Iowa, raising the possibility that Clinton could lose both key early nominating states of Iowa and New Hampshire, a new poll said Thursday. According to the survey by Quinnipiac University, Sanders now leads Clinton 41 percent to 40 percent among likely Democratic caucusgoers in Iowa. Sanders had trailed Clinton by 19 points in another Quinnipiac poll two months ago.

Clinton has already trailed Sanders by nine points in New Hampshire, the second voting state in the primary, according to a NBC News/Marist poll released Sunday.

Though Clinton still maintains double-digit leads nationwide in the Democratic field and remains the most favorite candidate of the Democratic establishment, the poll reminds many of her failed race in 2008, in which she also faltered in Iowa despite a strong start.

Once regarded as an underdog, Sanders has in recent weeks surged in poll numbers with his campaign mainly targeting income inequality.

"He is the candidate of the Democratic left, against his own party's bosses and their prized presidential candidate Secretary Hillary Clinton," said Quinnipiac pollster Peter Brown.

"Sanders has seized the momentum by offering a message more in line with disproportionately liberal primary and caucus voters," Brown added.

Though she has also made income inequality a central plank of her campaign, Clinton is viewed by some as less consistent in her claim to the subject due to close ties to Wall Street.

The poll came at a time when a beleaguered Clinton candidacy promoted many Democrats to consider an alternative to the former secretary of state, currently struggling to shed burden of mounting controversy around her private email setup.

After months of resistance to an apology, Clinton acknowledged Tuesday that her use of a private email system while helming the U.S. State Department was a "mistake", adding that she is "sorry" for it.

However, The New York Times said Thursday if Clinton continues to fail to reassure jittery supporters, senior Democrats are likely to implore other powerful Democratic figures to jump into the race to block Sanders, whose liberal policies are seen by the leadership as "disastrous" for the party to keep the White House in 2017.

Vice President Joe Biden, who is currently mulling over a possible candidacy, is reportedly on the list. Other possible names include former Vice President Al Gore, Senator Elizabeth Warren and Secretary of State John Kerry.

Citing several Democrats, the Times said among the four people, Biden and Kerry were considered by many as "especially well positioned" to enter the race late, given their experience, party support, fund-raising networks and name recognition.

Warren, a favorite of the progressive wing within the party, has repeatedly said she would not run for presidency despite supporters' push.

Also, earlier in August, an associate of the 67-year-old Gore told CNN the speculation that Gore was considering a candidacy was "groundless".

Kerry said recently he had no plans to run for presidency. However, in February, he also said "nobody ever says never."