What to Know Stockton's survey of 531 likely voters found Menendez with a 45 to 43 percent lead over Hugin, five weeks out from the Nov. 6 election.

Murray, arguably New Jersey's best-known independent pollster, called out the poll as having potentially damaging effects on trust in polls.

Last year, Menendez was put on trial on bribery charges, but the federal proceedings ended in a mistrial. Mistrust remains, the poll shows.

Incumbent U.S. Sen. Bob Menendez, seeking a third term, disputed the results of a poll released Monday that shows a close race with the Republican challenger, former pharmaceutical CEO Bob Hugin.

It's not unusual for a candidate to call out a poll that doesn't show his campaign in as favorable a light as he would like.

What is unusual is that another pollster also called into question the survey done by the Polling Institute at Stockton University's William J. Hughes Center for Public Policy.

Amounting to a duel between New Jersey universities, Patrick Murray of the Monmouth University Polling Institute said Stockton's survey has "serious problems" in its reliability.

Murray, arguably the Garden State's best-known independent pollster, went on to call out the poll as having potentially damaging effects on trust in voter surveys.

"Pollsters can have honest differences about methodological choices," he said in a long statement posted to his Twitter account on Monday afternoon. "... but there are times when clear methodological problems raise concerns about the enterprise."

A Stockton spokeswoman said Murray's public dispute shocked polling institute officials, but the institute stood by the survey in a statement.

"I respect the work done by Mr. Murray at Monmouth, but we stand by our poll results," executive director Michael Klein said. "We recognize the demographics in the poll are not entirely reflective of the population, and weight our results accordingly."

Stockton's survey of 531 likely voters found Menendez with a 45 to 43 percent lead over Hugin, five weeks out from the Nov. 6 midterm elections. Libertarian Murray Sabrin came in at 3 percent with an additional 8 percent of voters undecided.

“With a two-point lead falling within the poll’s margin of error, the Senate race at this point is up for grabs,” Klein said in releasing the poll.

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

Hugin has spent millions of his personal wealth on television and radio advertisements, controlling the message in the Senate race over the summer months. Some observers estimate he could spend up to $40 million before Nov. 6.

The Menendez camp said the senator's advertising campaign began in late August and his presence on television will continue to increase in the final month of the race.

Hugin's campaign hailed the Stockton poll as evidence that voters had begun paying attention to the Republican's message and that the incumbent's appeal in the liberal Garden State is waning.

But the Menendez campaign pointed to previous elections in which Democratic candidates significantly outperformed what Stockton polls found.

"The Stockton Poll historically underestimates Democratic performance; this is no different. At the same time in the race in 2016 and 2014, they undercut Hillary Clinton’s statewide performance by nine points and Cory Booker’s by seven, respectively, as each won by double-digit margins," the campaign said. "In 2012, Stockton had Senator Menendez with 52 percent, only to wind up with 59 percent en route to a 20-point victory."

Murray, in his Twitter statement, took exception with Stockton's methodology in several ways, including what he described as under-representation of voters aged 18-29 and blacks and Latinos.

He also questioned how Stockton weighs the advantage Democrats have over Republicans in New Jersey, based on the roughly 900,000-voter advantage that the Democratic Party has in the state.

Last year, Menendez’s federal bribery trial ended in a mistrial when the jury said it was hopelessly deadlocked on all charges against the New Jersey politician and a wealthy donor.

The Democrat was accused of using his political influence to help Florida eye doctor Salomon Melgen in exchange for luxury vacations in the Caribbean and Paris, flights on Melgen's private jet and hundreds of thousands of dollars in campaign contributions to organizations that supported the senator directly or indirectly.

Nearly 60 percent of voters polled said the corruption charges against Menendez are an extremely important or significant factor in their vote. But, 51 percent also said “a claim by that Hugin profited off an expensive cancer drug while CEO of a pharmaceutical company is an extremely important or significant factor in their votes,” according to the poll.

Menendez, the son of Cuban immigrants, served in the House from 1993 until he was appointed to fill a Senate vacancy in 2006. He has chaired the Foreign Relations Committee and was a major player in the unsuccessful bipartisan "Gang of Eight" effort to overhaul the nation's immigration laws in 2013.

Hugin, a native of Hudson County, graduated from Princeton University before entering the Marine Corps in 1976. He served for eight years. After earning an MBA from the University of Virginia, he went to work at J.P. Morgan. Over the years, he rose to managing director.

In 1999, he took over as chairman and CEO of a large pharmaceutical company called Celgene, based in Summit. He retired earlier this year.

"Any poll is just a snapshot in time," Klein, of Stockton, said. "We believe the Stockton Poll is reflective of where the Senate race is at this point."