The ongoing corruption investigation into Sen. Robert MenendezRobert (Bob) MenendezCongress must provide flexible funding for owners of repeatedly flooded properties Senate ethics panel resumes Menendez probe after judge declares mistrial Judge declares mistrial in Menendez bribery case MORE's (D-N.J.) relationship with a political donor has damaged the senator's favorability, according to a new poll.

A Quinnipiac University poll released Thursday found that 41 percent of voters disapprove of the job Menendez is doing, while 36 percent approve. That finding is a 15-point drop from a month earlier. In January, 51 percent of New Jersey voters approved of the job Menendez was doing, with 33 percent disapproving.

Menendez's current approval/disapproval split among New Jersey voters is also the lowest since August, 2011, when Menendez held a 39 percent favorable, 42 percent disapproval rating. 

Menendez is facing allegations that he improperly helped a donor who took him on private-plane trips to the Dominican Republic.

The senator last month acknowledged that he had taken previously unreported trips with the donor, Dr. Salomon Melgen, reimbursing him for two of those flights.

Menendez is alleged to have intervened on behalf of Melgen in a Medicare overbilling dispute and to have pressured officials to enforce a port security contract for a firm partially owned by the donor.

A report in The Washington Post last week said that the FBI was also investigating whether Menendez and Melgen consorted with prostitutes during those trips to the Dominican Republic.

Menendez has denied he was involved with prostitutes and blamed the allegations on a right-wing smear campaign.

Senate Democrats have stood by their colleague despite the probe. But the Quinnipiac poll suggests that Menendez's standing among voters has been harmed.

Forty-four percent said Menendez is not trustworthy, while 28 percent say Menendez is trustworthy, the poll also found.

Broken down by party affiliation, the poll found Menendez with 58 percent approval among Democrats and 19 percent disapproval. But that ratio is essentially flipped among Republicans. Menendez's disapproval among Republicans is at 63 percent, while his approval is at 18 percent. Among independents, Menendez holds a 45 percent approval rating and 31 percent disapproval.

Fifty-nine percent of those surveyed said the investigation makes them view Menendez less favorably, and 35 percent said the ongoing investigation does not affect their opinion.

Fifty-three percent said they are dissatisfied with how Menendez is handling the investigation, while 28 percent said they are satisfied. A majority, 67 percent, said the allegations should be investigated, while 23 percent believe the probe is fueled by partisan politics.

The poll was conducted from Feb. 13 to Feb. 17 among 1,149 registered voters and had a margin of error of 2.9 percentage points.