WASHINGTON -- Nearly one of every five Hispanic likely voters in New Jersey haven't decided whether to vote for U.S. Sen. Robert Menendez this fall, according to a poll released Monday.

While Menendez, D-N.J., led former Celgene Corp. executive Bob Hugin, 57 percent to 20 percent (Libertarian Party Murray Sabin had 3 percent) among Hispanic voters, the key number was 19 percent.

That was the percentage of Hispanics who remained undecided in the survey by Mason-Dixon Polling and Strategy for the Telemundo stations in New York, WNJU Channel 47, and Philadelphia, WWSI Channel 62.

"That was the one number that jumped out," said Brad Coker, Mason-Dixon's managing director. "He's kind of their guy, he probably hits 80-90 percent of their vote routinely, and it's one month out and you have 1 in 5 not convinced."

Coker suggested that Menendez's ethical problems may have turned off Hispanic voters. They said honesty and integrity in government was the third most important issue facing the country (15 percent), behind only the economy (21 percent) and immigration (18 percent).

Honesty in government had not been offered as a choice in Mason-Dixon polls of Hispanic voters in other states, but so many respondents in New Jersey named it as their top concern without prompting that it was added to this survey, Coker said.

"That issue isn't even on the radar screen anywhere else," Coker said. "It's pretty safe to say that has soured people, even people in the Hispanic community."

Through June 30, Hugin pumped $15.5 million of his own money into the campaign, most of it for television ads attacking Menendez, who was only the 12th senator ever indicted.

His trial ended up with a hung jury, and after a judge acquitted him of some counts, federal prosecutors declined to try him again. The Senate, however, severely admonished him for intervening with federal agencies on behalf of a friend an campaign donor, Dr. Salomon Melgen.

"It's a lack of enthusiasm," Coker said. "They just may say, 'Screw it' and not bother to vote."

Rep. Albio Sires, D-8th Dist., said he will expect Hispanic voters to eventually vote in big numbers for Menendez. He said the senator got a warm reception during Sunday's 43rd annual Hispanic Parade on Sunday in Hudson County.

"He got a great reception; nobody said boo or anything like that," Sires said. "People don't like to commit. They know who they're going to for vote but they don't like to say it on the phone."

Hispanics accounted for 13 percent of the electorate in the 2017 gubernatorial election, according to NBC News exit polls.

If the 19 percent of undecided Hispanics stay home, that could shave two or three points over Menendez's final vote percentage, Coker said.

That's the difference between Menendez and Hugin in a recent Stockton University poll, though Menendez led by 11 points in a Quinnipiac University survey and six points in a Fairleigh Dickinson University survey. Those three polls were of likely voters.

The issue with Hispanic voters mirrored Menendez's problem with his fellow Democrats in the FDU survey, in which 22 percent of Democratic likely voters said they were undecided in the race.

"He could still bring home the Democratic vote," Coker said. "I don't think it's doomsday yet. He's got 30 days and a heads up. But he's got to spend time rebuilding his base

"For every hour he's doing that, that's an hour he's losing going after the so-called swing voters."

Sires said there's nothing to worry about.

Even if Hispanics say they're undecided now, "that doesn't mean they're not going to go for him," Sires said. "At the end of the day, they'll all come home."

The poll of 625 registered Hispanic likely voters was conducted Oct. 1-4 and had a margin of error of 4 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.