A second poll in less than two weeks shows Sen. Bernie Sanders (I-Vermont) leading former Secretary of State Hillary Clinton in the race for the Democratic presidential nomination in New Hampshire.

Sanders leads Clinton, the presumed Democratic front-runner, by 7 points in the Granite State, according to the Public Policy Polling survey released Tuesday. A Franklin Pierce University/Boston Herald poll released almost two weeks ago also gave Sanders a 7-point lead.

Taken together, the polls are clear signs that Clinton will face a tougher-than-expected challenge in the first-in-the-nation primary state.

Sanders has become the most popular candidate with his or her base's voters, according to the PPP survey. The poll found that 78% of Granite State Democrats surveyed view him favorably, compared with just 12% who have a negative opinion of him. That compares with 63% of New Hampshire Democrats who have a favorable view of Clinton, compared with 25% who view her negatively.

Sanders has his biggest advantage with voters under the age of 65, leading with that group by 16 points.

“New Hampshire is really unique in the Democratic race,” said Dean Debnam, President of Public Policy Polling. “We still find Hillary Clinton well ahead everywhere else, but it’s clear at this point that there’s a real race in the Granite State.”

Overall, it's a huge shift from April, when Clinton led the Democratic field with 45% of the vote. Sen. Elizabeth Warren (D-Massachusetts), who was included in the poll but is not running for president, grabbed 23% of the vote then, while Sanders took 12%.

Democratic presidential candidate Hillary Clinton looks on as she speaks during a town hall meeting in Las Vegas, Nevada Thomson Reuters

Vice President Joe Biden, who will soon make a decision about whether to enter the race, was not tested in the PPP poll. But according to the FPU/Boston Herald poll released two weeks ago, 46% of New Hampshire Democrats said they want him to enter the race, while 42% want him to stay out. His favorability ratings have increased by 14 points since March among Democratic voters, according to that poll.

Clinton remains the overwhelming front-runner in both national polls and surveys of Iowa, which holds the first caucuses next year. According to a Real Clear Politics average of recent national and Iowa polls, she leads by an average of about 24 points. But she has been bogged down by lingering questions and a federal investigation into her use of a private email server as secretary of state.