The most recent Quinnipiac poll also found that 28 percent labeled Menendez "honest and trustworthy," compared with 44 percent who believe he is not. "Menendez took an overseas trip, and the poll numbers he left behind in New Jersey are dreadful," Maurice Carroll, director of the Quinnipiac University Polling Institute, said, adding: "The more they know, the less they approve."
The Quinnipiac poll found that 70 percent of New Jersey voters had read or heard something about the allegations, which have been supplemented by a steady trickle of new information.
The latest Quinnipiac findings contrast sharply with those of another survey, released a week earlier, that found the controversy had not significantly hurt Menendez, who is on a trip to Afghanistan and Pakistan.
The most prominent questions around Menendez center on two trips to the Dominican Republic he took on Melgen's plane. It took the senator more than two years to repay the $58,500 cost of the trips.
Then came word that Menendez also intervened with federal officials on two separate issues involving Melgen, who is reportedly being investigated for potential Medicare fraud.
Earlier, some conservative websites reported allegations that Menendez had trysts with prostitutes while visiting the Dominican Republic.
He has denied the prostitution accusations, and no solid evidence has emerged to back them up.
Menendez, who is traveling abroad as part of his new role as chairman of the Senate Foreign Relations Committee, has said that "no one has bought me."
His office declined to comment Thursday.
Menendez's approval rating is the lowest Quinnipiac has found for him since August 2011, when only 39 percent of voters gave him a thumbs-up. Still, Menendez rebounded to win reelection 15 months later, and he doesn't face voters again until 2018.
A Monmouth University/Asbury Park Press poll released one week earlier had better news for Menendez.
That survey found that 68 percent of New Jersey voters had heard about the scandal (a similar finding to Quinnipiac), but only 24 percent believed Menendez was involved in wrongdoing. Menendez had a 41-31 approval rating in the Monmouth poll - not great, but on the positive side.
One key difference: Quinnipiac limited its survey to registered voters, who tend to be more engaged with political news.
Quinnipiac surveyed 1,149 registered voters, with a margin of error of 2.9 percent. The survey was from Feb. 13 to Sunday.
Monmouth polled 803 New Jersey adults, with a margin of error of 3.5 percent. Its survey was done Feb. 6 to 10.
Quinnipiac found that Newark Mayor Cory Booker has a 59-11 approval rating - 47-24 among Republicans - affirming his status as the favorite to replace retiring Democratic Sen. Frank J. Lautenberg in 2014.
Contact Jonathan Tamari
at firstname.lastname@example.org or follow on Twitter @JonathanTamari. Read his blog, "CapitolInq," at www.philly.com/CapitolInq.