Democratic challenger Andy Kim declared victory Wednesday over Republican U.S. Rep. Tom MacArthur, R-3, although the tight race for the 3rd Congressional District remained uncalled.

The district, which stretches between Burlington County in the Philadelphia suburbs and Ocean County along the shore, has largely been held by the GOP for the past three decades.

The AP has not called the race. It was among the most closely watched in the country.

Unofficial Burlington County returns posted late Wednesday showed Kim with a more than 2,000 vote lead over the two-term incumbent. MacArthur said Wednesday night via Twitter that he was not ready to concede the race.

"This has been a hard fought campaign and like Andy Kim, I'm ready to see it come to an end," MacArthur's statement said. "I have always said that I will be guided by the voters of the district and there are nearly 7,000 more of them who haven't been heard from yet. We must ensure that their votes - and all votes - are counted in a transparent way that protects the integrity of the election."

Officials have said they are still planning to count provisional ballots and additional mail-in ballots postmarked by election day that continue to arrive.

Burlington County Board of Election Chairman Joe Dugan said there were about 26,000 mailed-in ballots.

In the GOP-leaning part of the district, Ocean County Board of Election official Jason Varano says roughly 31,000 mail-in ballots are already reflected in results posted online.

Officials say provisional ballots also remain to be counted.

MacArthur backed Trump more often than any other member of the New Jersey congressional delegation, according to Nate Silver's FiveThirtyEight.

He helped save the president's attempt to repeal the Affordable Care Act, also known as Obamacare, by crafting a compromise for states to opt out of ending preexisting-condition requirements for insurance companies. The provision enabled patients with chronic, ongoing illnesses to not be denied insurance coverage.

But MacArthur, 58, a former health insurance executive, stressed he's someone who has worked for bipartisan solutions in Congress and labeled Kim's campaign as a protest vote for Trump.

He criticized Kim for being a liberal Democrat and for allegedly benefiting from television commercials paid for by a political action committee of U.S. House Democratic leader Nancy Pelosi. Kim had made a campaign promise to not accept corporate PAC money.

Kim, 36, who had never run for elected office before, was a civilian advisor to military leaders in Afghanistan and Iraq and national security aide in Democratic President Barack Obama's administration.

MacArthur accused Kim of embellishing his resume and labeled him as an "entry level" employee during his tours abroad.

Kim criticized MacArthur for siding with Trump on the Obamacare repeal, which eventually died in the U.S. Senate with former Sen. John McCain's deciding vote. Kim also attacked MacArthur for voting for Trump's tax-cut plan which became law and eliminated all but $10,000 in deductions for state and local taxes, a favorite deduction for residents in the Northeast part of the country, especially New Jersey.

The 3rd district includes Burlington and Ocean counties and the 40,000-acre Joint Base McGuire-Dix-Lakehurst. The major military facility has been an economic engine in the region since it opened in 1938.

Democrats have captured at least 10 of 12 House seats in New Jersey, flipping three of them.

The Associated Press contributed to this report.

Bill Duhart may be reached at bduhart@njadvancemedia.com. Follow him on Twitter @bduhart. Find NJ.com on Facebook.

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