So how close is the race between Democratic U.S. Sen. Robert Menendez ahead of Republican Bob Hugin?

In a Quinnipiac University Poll released Wednesday, Menendez, D-N.J., led Hugin by 11 points (53-42 percent) among likely voters.

But that came after two other polls showed a much closer race.

A Fairleigh Dickinson University poll released earlier Wednesday had Menendez up by 6 points with pollsters cautioning it may be closer because of the margin of error, and the Democrat was up by just 2 points in a Stockton University survey released on Monday.

What gives?

"There are different choices that pollsters make on who to call and what they expect the final demographics of the voting population on Election Day to look like," said Ben Dworkin, director of Rowan University's Institute for Public Policy and Citizenship.

"Those choices made by pollsters can have significant effects on the final results."

That helps explain why Monmouth University pollster Patrick Murray criticized the Stockton poll, which he said undersampled some key voting blocs.

The bottom line, though, is that Hugin has never led in any poll. The latest poll marked the first time Menendez polled over 50 percent.

"This is a strong Democratic state in a strong Democratic year and Bob Menendez is a strong Democrat," Dworkin said. "While people may not like Bob Menendez, they clearly want a Democrat in the seat who's going to stand up to run."

Even so, the Cook Political Report on Thursday said Menendez now was only slightly favored to win.

"His lead is probably in the mid-to high single digits," wrote Jennifer Duffy, the Senate race analyst for Cook, a Washington-based publication that tracks the races.

"This race is more competitive than a Senate contest in a good year for Democrats in a state as blue as New Jersey should be," she wrote. "This is entirely on Menendez and the baggage he brings into the race. He maintains the advantage going into the final stretch, but the race is worth watching."

In the Quinnipiac poll, Menendez received the support of 93 percent of Democratic voters. In the FDU survey, however, he was backed by just 73 percent, with 22 percent of Democrats undecided.

"Sen. Robert Menendez has the advantage of representing very blue New Jersey, where there are many more Democrats than Republicans," said Mary Snow, an analyst for the Quinnipiac poll.

Still, Hugin, the former Celgene Corp. executive, has made this race competitive, largely through his self-funded multimillion-dollar ad campaign attacking Menendez, and the senator's own unpopularity.

More than half of likely voters, 53 percent viewing him unfavorably compared with a favorable rating of 34 percent. Hugin was viewed favorably by 35 percent, with 27 percent expressing an unfavorable opinion and 34 percent saying they didn't know enough about him.

Menendez -- who was "severely admonished" by the Senate Ethics Committee and stood trial on federal corruption charges (after a mistrial, a judge acquitted him of some allegations and prosecutors dropped the rest) -- was viewed as honest by just 25 percent of likely voters. A majority, 59 percent, said he was not honest.

"New Jersey likely voters may prefer Sen. Menendez over Republican challenger Bob Hugin, but they certainly make it clear they are not fond of Menendez," Snow said.

Menendez built his lead with the support of women, who backed him, 57 percent to 38 percent. Men gave 48 percent of their support to both candidates. Hugin went to court to prevent women from joining Princeton University's famed eating clubs.

The senator also benefitted by New Jerseyans' antipathy toward President Donald Trump.

Only 35 percent approved of Trump's performance in office, while 62 percent disapproved. In addition, 63 percent said Congress should be "more of a check" on the president, while 28 percent said the legislative branch was doing enough.

Hugin contributed the maximum $5,400 to Trump's campaign in 2016 and another $233,200 to the Republican National Committee that helped elect him.

Menendez's had a 46 percent job approval rating, with 44 percent disapproving of his performance in office. U.S. Sen. Cory Booker, D-N.J., on the hand, had 58 percent positive and 37 percent negative job approval ratings.

The Quinnipiac poll of 1,058 likely voters was conducted Sept. 25-Oct. 2 and had a margin of error of 4.1 percentage points.

Jonathan D. Salant may be reached at jsalant@njadvancemedia.com. Follow him on Twitter @JDSalant or on Facebook. Find NJ.com Politics on Facebook.