The poll, conducted by Harper Polling, a firm run by former National Republican Congressional Committee pollster Brock McCleary, pegs public perception of Menendez as decidedly negative.

Only 32 percent of those polled approved of the job he's doing, while 48 percent disapproved. That's a stark difference from a recent nonpartisan Quinnipiac Poll, which showed his approval rating as above water.

Wednesday's Quinnipiac poll pegged his job approval at 40 percent, while 37 percent disapproved.

That seemed to indicate a rebound from February, when prostitution allegations against Menendez continued to develop. He is also under investigation for potentially inappropriately advocating for the business interests of a political donor.

There's indication in the Harper Polling survey that, while the investigation into his relationship with a donor might be having little effect on his job approval, the prostitution allegations may have caused a harder hit.

While the Quinnipiac poll asked respondents specifically about his potential ties to the political donor, the Harper Polling survey merely asks if the "information" respondents have heard about Menendez in the news recently affects their opinion of him, without offering details.

With unspecified details, 48 percent of respondents say the news they've heard about the senator has made them look at him less favorably, while 32 percent say they're unsure whether the news they've heard affects their opinion.

Though the investigation into Menendez's ties to a donor is still in its early stages, and Menendez has made no indication he plans to resign from the Senate, Harper Polling surveyed on a potential special election in such a situation, and showed that New Jersey Senate GOP Leader and former Gov. Tom Kean would lead a Republican primary, while state Sen. Richard Codey would lead a Democratic primary.

The survey's results, however, are atypical for a state as blue as New Jersey. It also shows a generic Republican candidate in a Senate race breaking near even with a generic Democratic candidate, unlikely in a state that backed President Obama in 2012 by double digits.

GOP Gov. Chris Christie, who is expected to cruise to reelection, also posts a strong approval rating in the survey. And nearly 50 percent say the fact that he wasn't invited to the Conservative Political Action Conference makes them less likely to vote for him.

The survey was conducted from March 24-25 among 760 likely voters and has a margin of error of 3.55 percentage points.

--This piece was updated at 12:28 p.m. to reflect Codey's lead in a hypothetical Democratic primary.