New Jersey's tense U.S. Senate race between Democratic incumbent Robert Menendez and Republican challenger Bob Hugin is a dead heat with only five weeks until Election Day, according to a new poll.

Menendez leads Hugin by a mere two percentage points, 45 percent to 43 percent, in the Stockton University poll released Monday morning -- which is within the poll's margin of error.

Libertarian candidate Murray Sabrin gets 3 percent of the vote, while other candidates and undecided voters make up 8 percent heading into the Nov. 6 election.

"With a two-point lead falling within the poll's margin of error, the Senate race at this point is up for grabs," Michael W. Klein, the interim executive director of the William J. Hughes Center for Public Policy at Stockton University, said in a statement.

"Bob Hugin has been attacking Senator Menendez on ethics with a heavy advertising campaign," Klein added. "However, with so many voters still unfamiliar with the Republican, Menendez will likely try to define his challenger in negative terms."

Though other polls have shown a closer-than-expected battle between Menendez and Hugin, this is the first to show a razor-thin margin in the critical race.

A Menendez loss, once considered unthinkable, could jeopardize Democrats' chances of re-taking control of the U.S. Senate, which Republicans control by only two seats -- 51 to 49.

No Republican has been elected to the U.S. Senate in New Jersey since 1972. Registered Democrats outnumber registered Republicans by a nearly 2-to-1 margin in the state.

Plus, Democrats have been hoping to leverage Republican President Donald Trump's unpopularity in New Jersey into tightening their control of the state's congressional delegation. The Stockton poll shows 64 percent of likely voters say Trump is doing a poor or fair job.

But Menendez, who is vying for a third full term, has been hurt by federal corruption charges he beat earlier this year. Though Menendez was acquitted thanks to a hung jury and the federal government dropped all charges, he was also "severely admonished" by a Senate ethics panel.

Monday's poll shows 59 percent of likely voters say the charges are an extremely important or significant factor in their vote.

Meanwhile, 51 percent say the allegations that Celgene, the pharmaceutical company Hugin once ran, raised prices on drugs for cancer patients are important. Hugin, a multimillionaire, is now retired.

Menendez, Hugin, and their allies have poured millions into a series of back-and-forth bruising campaign ads highlighting the corruption charges and drug prices, respectively.

Menendez has also tried to score points by painting Hugin as a supporter of Trump supporter.

Hugin said Monday the poll is "no surprise."

"Whether you're a Democrat, Republican, or independent, voters want a senator who will put New Jersey first and represent them with honor and integrity," the Republican nominee said in a statement. "That's why a growing number of Democrats are publicly endorsing my campaign."

But Menendez's campaign said Stockton's polls "historically underestimate Democratic performance."

"No one has fought harder and longer and delivered more for New Jersey than Bob Menendez," the campaign said. "At the end of the day, New Jerseyans will choose a proven fighter who will stand up to Trump's dangerous policies, not a Trump, Christie Republican like Bob Hugin who made a fortune ripping off cancer patients and will never have our back and will just be another vote for Trump's dangerous policies."

At the same time, at least one prominent pollster took issue with Stockton's methodology.

In a statement issued late Monday, Patrick Murray, director of the Monmouth University Polling Institute, said there were "serious problems" with the way the Stockton conducted the survey.

Murray argued the way data was weighed seemed off the mark, with a too-small sample of younger and minority voters.

I do not make this comment on the Stockton poll lightly. But I feel this practice can undermine the credibility of the good work done not only by Monmouth, but also Marist, Siena, Quinnipiac, Eagleton, FDU, etc. pic.twitter.com/6jVxt51zLG — Patrick Murray (@PollsterPatrick) October 1, 2018

The Stockton poll also found Menendez is viewed favorably by 30 percent of likely voters and unfavorably by 54 percent, while 6 percent are unsure. Only 10 percent are not familiar with the senator.

Hugin is viewed favorably by 34 percent and unfavorably by 21 percent. But 43 percent are not familiar with him.

The poll was conducted via telephone from Sept. 19-27 with 531 likely New Jersey voters. The margin of error is plus-or-minus 4.25 percentage points.

Brent Johnson may be reached at bjohnson@njadvancemedia.com. Follow him on Twitter @johnsb01. Find NJ.com Politics on Facebook.