TRENTON -- With Election Day just five weeks away, a new poll shows Democratic nominee Phil Murphy leading Republican Kim Guadagno by 14 percentage points in the race to succeed Gov. Chris Christie -- a tighter margin than those in recent similar surveys.

The Monmouth University Poll released Tuesday shows 51 percent of likely New Jersey voters back Murphy, a former U.S. ambassador to Germany and ex-Goldman Sachs banking executive. Meanwhile, 37 support Guadagno, Christie's lieutenant governor.

Five other candidates draw 2 percent, while 9 percent of voters are undecided.

Monmouth's last poll, from July, showed Murphy with a 27-point lead over Guadagno.

Patrick Murray, the head of the Monmouth University Polling Institute, notes that this survey is not directly comparable to that one because it's the group's first in the race taken of voters who are actually likely to cast ballots in the Nov. 7 election -- not the broader pool of all registered voters in the state.

Still, a Quinnipiac University poll of likely voters from earlier this month showed Murphy up by 25 points, while a Suffolk University/USA Today Network survey of likely voters from last week had him ahead by 19 points.

Murray, however, said Murphy's lead in Tuesday's Monmouth poll is "still formidable."

"While Guadagno may have an opportunity to break through, the fact that Murphy's support is over 50 percent makes that task very difficult," Murray said.

The survey also found nearly half of likely voters have not formed an opinion about either Murphy or Guadagno even though the election is a little more than a month away. Only 33 percent have a favorable view of Murphy, while 31 percent have a favorable view of Guadagno.

"Low name recognition of New Jersey gubernatorial candidates this late in the game is not unprecedented because the state lacks its own media market," Murray said. "However, it is unusually low this year. The campaigns simply can't break through with the political noise coming out of Washington."

The poll, conducted Thursday to Sunday, also shows a mere 23 percent of likely voters say New Jersey is headed in the right direction.

Plus, Christie and President Donald Trump, both Republicans, score low marks. Christie's approval rating is 22 percent, while Trump's is 33.

And that, the poll found, is affecting Guadagno.

About 29 percent of voters say knowing Guadagno is Christie's lieutenant governor makes them less likely to vote for her -- nearly double the number (16 percent) who say this makes them more likely to back her. Most (54 percent) say it makes no difference.

"The double whammy of Trump and Christie has not helped the Republican brand in New Jersey," Murray said. "While Gaudagno's current position as Christie's number two is not a death blow to her chances, it certainly isn't helping."

In addition, the focus of Guadagno's platform -- cutting property taxes -- doesn't seem to be connecting with voters. Only 12 percent say they have heard about her plan. Just 6 percent say they have heard about a property tax plan from Murphy, even though he has not offered a specific proposal.

Even if Guadagno does gain traction on taxes, it may not make a difference. Seventy percent say they are likely to see any plan to cut taxes as a campaign ploy, while only 20 percent say they would see it as as genuine effort.

"I just think voters have heard too many promises for too long and simply tune out all candidate rhetoric on the issue at this point," Murray said. "Guadagno has little time left and a tall hill to climb if she is going to break through with her plan."

As for Guadagno's effort to link Murphy to his past at Wall Street firm Goldman Sachs? Only 28 percent say Murphy's time at the company is something they associate with him. And 70 percent say it has no impact on their vote.

There are also five third-party or independent candidates running: Libertarian nominee Peter Rohrman, Green Party nominee Seth Kaper-Dale, and independents Gina Genovese, Matthew Riccardi, and Vincent Ross.

Christie's 22 percent approval rating is higher than marks he's received in recent polls that have put him in the mid-teens -- including an historically low 15 percent rating in a July Monmouth poll. But again, the two are not comparable because this survey relies on the smaller pool of likely voters, while the earlier poll surveyed New Jersey adults.

The poll released Tuesday was conducted via telephone from Sept. 28 to Oct. 1 with 452 New Jersey residents who are likely to vote in the election. The margin of error is plus-or-minus 4.6 percentage points.

Brent Johnson may be reached at bjohnson@njadvancemedia.com. Follow him on Twitter @johnsb01. Find NJ.com Politics on Facebook.