It's primary election day Tuesday in New Jersey, when registered Democrats and Republicans will have the opportunity to choose party nominees for U.S. Senate, U.S. House, and a variety of county and municipal offices.

This year, the races for U.S. House nominations are particularly active across the state, as Democrats sense a legitimate chance to pick up a congressional seat or two and Republicans seek the strongest candidates to keep competitive districts in their party's hands.

New Jersey has a closed primary system, meaning only voters affiliated with a political party can participate in its candidate-selection process. But there is an opening for unaffiliated voters, those not registered with a party: In congressional and state primaries, they are allowed to declare an affiliation right at the polls in order to participate.

About 41 percent of the state's 5.8 million registered voters are unaffiliated, according to the New Jersey Department of Elections.

Start with finding or confirming your polling place if you are unsure where to go. Polls will be open statewide from 6 a.m. to 8 p.m.

New Jersey congressional districts.
Ballotpedia.org
New Jersey congressional districts.

Despite Democrats' domination of New Jersey politics in general, the state's 12 congressional districts are, at this point, relatively evenly distributed between the two major parties: seven U.S. House seats are held by Democrats, five by Republicans. That's because, unlike in many other states, such as Pennsylvania, New Jersey uses a bipartisan commission to draw U.S. House district boundaries rather than letting legislators do it. This tends to tamp down the worst gerrymandering mischief.

Now, because of a pair of retirements of moderate longtime Republican representatives and the surge of anti-Trump energy on the left, anywhere from two to five additional seats seem to be in play for the Democrats, depending on which analyst is doing the figuring.

First Congressional District: Norcross faces 2 challengers

The First, which contains most of Camden County, a sliver of Burlington County and part of Gloucester County, is overwhelmingly Democratic. Incumbent U.S. Rep. Donald Norcross, a Democrat, faces primary opposition from Rob Carlson of Collingswood, who works in information technology, and Scott J. Tomaszewski, an electrician who says Washington needs "more boots and less suits."

Second Congressional District: Democrats’ best shot at a GOP seat?

Democrats got a boost when Republican U.S. Rep. Frank LoBiondo announced his retirement in November, creating an open seat in the Second District as he joined an exodus of moderate GOP House members.

Sprawling across South Jersey, the Second supported Barack Obama twice, but President Trump carried it by 5 percentage points in 2016.

Democratic bosses, national and local, quickly coalesced around moderate  State Sen. Jeff Van Drew of  Cape May County, who has voted against tougher gun laws and same-sex marriage.

Though party strategists say he's a good fit for the district, some Democrats think Van Drew is little better than a Republican. Two progressive candidates, retired teacher Tanzie Youngblood and former U.S. Senate aide Will Cunningham, are challenging him in the primary, as is Nate Kleinman, a farmer and political activist who participated in Occupy protests and once ran for Congress in southeast Pennsylvania.

The head of the national GOP's congressional campaign arm characterized the Second District as a weak spot in candidate recruitment, though he later walked back those remarks. Early on, party leaders had hoped popular state Sen. Chris Brown (R., Atlantic) would run, but he passed.

The four GOP candidates running for the nomination are Hirsh Singh, an engineer who lost a race for the gubernatorial nomination last year and says he wants to embrace Trump's agenda; former state Assemblyman Sam Fiocchi; former FBI agent Robert Turkavage; and attorney Seth Grossman, leader of an anti-tax group called Liberty and Prosperity.

Third Congressional District: General election already set

The general race is already set in the Third, which includes most of Burlington County and parts of Ocean County, and the likely nominees have been raking in campaign money and already trading blows.

U.S. Rep. Tom MacArthur at a contentious town meeting in Willingboro in the spring of 2017.
Tom Gralish
U.S. Rep. Tom MacArthur at a contentious town meeting in Willingboro in the spring of 2017.

Republican U.S. Rep. Tom MacArthur, reelected to a second term in 2016 by 20 percentage points in the competitive district, faces a challenge from Democrat Andy Kim, of Marlton, a former national security adviser in the Obama administration.

Democrats believe MacArthur is vulnerable because he has provided some crucial help in advancing Trump's agenda, including negotiating a deal to keep alive the effort to repeal the Affordable Care Act. (The repeal failed in the Senate.) For that, MacArthur was forced to step down from a group of moderate House Republicans and drew protests. The representative also backed the Trump tax cuts, which capped the  deduction for local property taxes widely used in New Jersey, which has the highest such levies in the country.

The MacArthur campaign has attacked Kim as really residing in Washington, D.C., citing a property tax break he enjoys on a $1 million condo there — and says the challenger has exaggerated his resume.

Both candidates are well-funded, and the Cook Political Report rates the race as competitive, but leaning toward MacArthur.

Andy Kim, a Democrat who grew up in Marlton, is running for Congress, against Republican U.S. Rep. Tom MacArthur.
Julio Cortez
Andy Kim, a Democrat who grew up in Marlton, is running for Congress, against Republican U.S. Rep. Tom MacArthur.

Fourth Congressional District: Dems choosing nominee with hopes of unseating longtime GOP representative

In 1980, Republican Rep. Chris Smith won election to the U.S. House, helped by Ronald Reagan's strong showing in the district — and the indictment of longtime Democratic incumbent Frank Thompson in the Abscam scandal. Smith has served for nearly 38 years; he is known for his leadership against abortion rights, as well as his work on international human rights issues, including human trafficking.

U.S. Rep. Chris Smith (R.,N.J.) campaigning Saturday in Monmouth County. (AP Photo/Julio Cortez)
Julio Cortez
U.S. Rep. Chris Smith (R.,N.J.) campaigning Saturday in Monmouth County. (AP Photo/Julio Cortez)

This year, Democrats are hoping that anti-Trump sentiment and a fired-up liberal base can help them flip the Fourth, which includes parts of Ocean, Monmouth and Mercer counties. First, they need to choose a nominee.

Party leaders have gotten behind Josh Welle, 37, a veteran Navy officer and founder of a technology software company He is opposed by Jim Keady, a liberal activist and former Asbury Park councilman most famous for the time former Gov. Chris Christie told him to "sit down and shut up" as he protested the state's response to Superstorm Sandy in 2014.

Yes, there is a contested primary in each party Tuesday, but incumbent Democratic Sen. Robert Menendez, 64, and Republican challenger Bob Hugin, 63, already are slashing away at each other in what is expected to be a particularly brutish general election campaign. The national backdrop: a fight for control of the Senate, narrowly held by the GOP, 51 seats to 47 seats.

Voters go to the polls Tuesday just weeks after the Senate Ethics Committee "severely admonished" Menendez for accepting valuable gifts from a campaign donor, and then using his position to advance the personal interests of Salomon Melgen, a Florida eye doctor convicted of one of the largest Medicare frauds in history.

A federal prosecution of Menendez on corruption charges ended in mistrial late last year, and authorities later dropped the charges against him. Hugin, a millionaire former pharmaceutical CEO, has aired TV ads calling Menendez a "disgrace."

In the primary, Menendez is challenged by Lisa McCormick, a publisher of community newspapers who briefly ran for the Democratic nomination for governor last year.

Hugin has his own baggage: his former firm, Celgene, settled a case for $280 million over allegations that it promoted cancer drugs that had not been approved by the FDA. As is customary in such settlements, the company admitted no wrongdoing.

Brian Goldberg, an IT engineer and construction executive who casts himself as a Trump acolyte, is challenging Hugin for the GOP nomination.

New Jersey Sen. Bob Menenedez, Democratic incumbent, at left. Republican challenger Bob Hugin at right.
Julio Cortez
New Jersey Sen. Bob Menenedez, Democratic incumbent, at left. Republican challenger Bob Hugin at right.

New Jersey Sen. Bob Menenedez, Democratic incumbent, at left. Republican challenger Bob Hugin at right.

Here is information on local races on the ballot Tuesday: