TRENTON -- A new poll shows Democratic nominee Phil Murphy leading Republican nominee Kim Guadagno by 13 percentage points in the race to succeed Chris Christie as New Jersey's governor -- a noticeably smaller margin than other surveys have found.

Murphy, a former U.S. ambassador to Germany and ex-Goldman Sachs banking executive, has the support of 42 percent of registered Garden State voters, according to the Fox News poll released Thursday. Guadagno, Christie's lieutenant governor, draws 29 percent.

Other polls in the race have shown Murphy up by at least 20 percentage points. Last week, a Quinnipiac University survey found him with a 25-point lead.

One distinction: That Quinnipiac poll surveyed likely voters, while the Fox poll surveyed the broader pool of registered voters.

Past polls have also shown Murphy nabbing at least 50 percent of the electorate.

But the Fox survey found 19 percent of the state's voters -- or 1-in-5 -- remain undecided less than two months before the Nov. 7 election. That includes 14 percent of Republicans, 16 percent of Democrats, and 33 percent of independents.

"While Murphy has a sizable advantage, many voters haven't tuned in yet," said Democratic pollster Chris Anderson, who conducts the Fox News survey with Republican pollster Daron Shaw.

Anderson added that "if the undecided voters break disproportionately for Guadagno, then the race could tighten significantly."

Still, a higher percentage of Democrats support Murphy (74 percent) than Republicans do Guadagno (68 percent).

The poll also found:

* 62 percent of voters are unhappy with how things are going in the state, while only 37 percent are satisfied.

* Taxes are the biggest concern for voters, with 34 percent of voters saying so. And those who rank taxes as their top concern are more likely to vote for Guadagno than Murphy, 43 to 31 percent.

* The economy is the No. 2 issue for voters (13 percent), following by drugs and drug addiction (9 percent) and education and health care (both at 8 percent).

* 54 percent of voters disapprove of the job President Donald Trump, a Republican, is doing, while 40 percent approve. Undecided voters are split. That's similar to other polls in the state, where registered Democrats outnumber registered Republicans nearly 2-to-1.

* Almost three-quarters (74 percent) say Trump will not be a factor in their vote in the governor's race.

The poll was conducted via phone from Sept. 17 to 19 with 804 New Jersey voters. The margin of error is plus-or-minus 3.5 percentage points.

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