At play is the seat that already has seen the region's most brutal primary, when Republican Tom MacArthur beat Steve Lonegan for the chance to replace U.S. Rep. Jon Runyan (R., N.J.).
Now, national Democrats are taking aim at MacArthur as they try to elevate Burlington County Freeholder Aimee Belgard in a district that includes much of Burlington and Ocean Counties.
The district was named as one of Democrats' seven best pickup opportunities by U.S. Rep. Steve Israel (D., N.Y.), head of the Democratic Congressional Campaign Committee, and the group followed up Tuesday with a hard-hitting attack, one of its first two television ads of the general election.
"Democrats are certainly targeting New Jersey 3 over the other ones, and that makes sense," said Kyle Kondik, managing editor of Sabato's Crystal Ball, a political handicapping site. "It's a fairly narrow list of offensive targets this time."
National Republicans have also named MacArthur one of their top-tier candidates and have helped his campaign in early sparring with Belgard.
The race has become more crucial to Democrats as potentially competitive districts based in Bucks, Chester and Atlantic Counties have seemed to move in the GOP's favor. Local factors - Republicans' superior fund-raising, GOP incumbency in two of the races, and a rocky Democratic primary season - combined with President Obama's sagging poll numbers have tilted the playing field.
But Democrats see a sliver of hope in Runyan's district. Even though Republicans have dominated House races there, Obama twice won the Third, and the incumbent is retiring.
The national party's ad assails MacArthur for the work of his former company, York Risk Services, which helped insurers process claims. It plays on three instances in which his firm was accused of shorting individuals or institutions hit by hurricanes or wildfires.
The ad doesn't mention those cases directly. Instead, it opens with an image from the aftermath of 2012's Hurricane Sandy, which battered the South Jersey district, but which MacArthur had nothing to do with professionally. He sold his insurance business years earlier.
MacArthur called the ad and its claims "really, really deceptive," and accused Belgard of being an "empty candidate" who has ducked scrutiny and stuck to Democratic scripts.
FactCheck.org, a nonpartisan group affiliated with the University of Pennsylvania's Annenberg Public Policy Center, criticized the ad under the headline "DCCC Deceptions."
"There's a long list of serious issues that deserve discussion," MacArthur said in an interview, listing jobs, health care and immigration among others. "I've got my ideas about how they should be handled. The Democrats have different ideas. But I don't think Aimee Belgard has any ideas."
Belgard said the ad "raises valid concerns" about MacArthur's past as chief executive of York.
Asked whether it was fair to include images from Sandy, she said, "I would have to direct that question to the DCCC," which created the spot.
A spokeswoman there stood by it.
Belgard has cast MacArthur as an opportunist who moved from North Jersey to the district only after Runyan announced he wouldn't run and a multimillionaire out of touch with everyday voters.
"Washington is broken. The corporate interests are continuing to profit while more and more of the burden is shifted to the middle class," Belgard said. "The middle class needs an ally in Washington, and that's what I'll be."
After the ad ran, MacArthur added "hypocritical" to his criticism of Belgard, pointing out that she spent 16 years as an attorney working for insurers.
Belgard, in an interview, agreed with the suggestion that lawsuits don't necessarily mean the defendants did something wrong, but added, "There was a history of his company having been sued over time for issues of unsavory practices."
She cited the three cases first raised by Lonegan in the primary. Each stemmed from incidents that happened while MacArthur was at York but were settled without any finding of wrongdoing after he sold the firm.
He said York faced only a handful of suits out of millions of claims it handled.
While the attacks on style and background have been sharp, both candidates have stuck to the center when it comes to policy in the moderate district.
On immigration, the issue that roiled Congress before its August recess, each said he or she supports stronger steps to secure the border but also would back a tough but fair path to citizenship for people already in the United States illegally.
The sharpest differences emerge in their attitudes toward business.
MacArthur touts himself as a man who built a small business into one that employed thousands and criticized Obama for "picking winners and losers" in private industry, especially in health care.
"Government is trying to control how industry is run, and it's a mistake," he said.
Belgard said she would fight to close "tax loopholes" that allow businesses to move jobs overseas.
She said she would use the money to expand middle-class tax credits and help students afford college.
Belgard had raised nearly $826,000 by June 30, the latest reporting date, a strong showing for a first-time House candidate, but MacArthur had poured $3 million of his own money to his primary and general election campaigns.
He said he planned to focus on issues, but "I'm not going to take her attack lying down."
"I have resources," he said, "so she's not going to outspend me."