The race for November is officially on in New Jersey's Third Congressional District, where Republican U.S. Rep. Tom MacArthur and Democrat Andy Kim will face off for the competitive U.S. House seat — one of many races nationally in which Democrats hope to oust a Trump-allied incumbent.

Neither candidate was challenged in the primary for the competitive district, which includes most of Burlington County and swaths of Ocean County. MacArthur, for whom Trump held a fundraiser at his Bedminster golf course last summer, and Kim, a former national security adviser in the Obama administration, already have been trading jabs.

>> READ MORE: New Jersey primary elections results: Live updates

MacArthur was first elected as a moderate conservative, but has aligned himself with President Trump on issues including the attempted repeal of the Affordable Care Act and Trump's tax cuts, which capped the federal deduction for local property taxes. Though MacArthur was reelected by a wide margin in 2016, Democrats hope anti-Trump momentum will bring their voters to the polls.

The district is split between the eastern part in Ocean County, where Trump has a conservative base, and the western part in Burlington County, where there are pockets of Democrats who often don't turn out to vote, said Patrick Murray, an analyst at Monmouth University.

If they do turn out — as similar liberal populations have in recent special elections in other states — it could swing the race in Kim's favor.

"It's a combination of persuasion on local issues plus turnout on national issues," Murray said. "The kind of voter he's trying to turn out, Kim, will be Democrats who don't vote in midterm elections. That's where we've seen the surge from in other states — Democrats who will only vote in presidential elections but are riled up about Donald Trump and are coming out to vote in these midterm and special elections."

Kim's skill as a candidate is untested. Also uncertain is whether Trump may campaign for MacArthur, which might not help much in New Jersey. Already, MacArthur has raised $1.9 million and Kim $1.4 million, according to public filings.

"This race could be a lot more competitive than a lot of people think," Murray said.