New York's 3rd Congressional District is hosting the first closely watched contest of 2024, with political experts saying that the results of Tuesday's special election could offer some early signs of how swing-seat suburban voters are feeling as the presidential race begins to ramp up.

Former Rep. Tom Suozzi, a well-known Democrat in the area who used to represent the district before leaving for a failed gubernatorial bid in 2022, is facing Republican Mazi Pilip, a Nassau County legislator with a smaller profile.

The race, which has attracted millions of dollars and major New York politicians, is playing out on Long Island, a key battleground for House control later this year and a barometer, experts said, for messaging on crime, immigration and more.

Who's running -- and how are they doing it?

Tuesday's special election was triggered by disgraced Republican Rep. George Santos' expulsion in December.

There wasn't a primary, and Suozzi and Pilip were both essentially handpicked by their respective parties to run for the seat.

Suozzi, a former three-term representative, mayor and county executive, boasts broad name recognition in the district -- an asset for him as he seeks to run on his own brand rather than that of a national party led by an unpopular president.

Pilip, meanwhile, is an Ethiopian-born Jew who served in Israel's military, a high-profile resume given the current war against Hamas in Gaza. While a current officeholder herself, she cuts a lower profile than Suozzi and has made fewer campaign stops than he has.

Suozzi has sought to distance himself from President Joe Biden, who has long been grappling with poor approval ratings nationwide. He's especially cast himself as tough on illegal immigration, fighting back against attacks from Pilip that he supports more lax border controls. The issue has become a local flashpoint as New York City sees an influx of immigrants and asylum-seekers.

Suozzi has particularly hit Pilip for opposing a recent bipartisan immigration bill in the Senate that would tie foreign aid to heightened border security, noting he would have supported the legislation, which also won the endorsement of the union that represents front-line Border Patrol agents. (That same union is supporting Pilip over Suozzi.)

Suozzi has also gone after Pilip for, he said, dodging on abortion access in order to appeal to voters. The issue took on heightened importance in races across the country after the Supreme Court revoked constitutional protections for the procedure in 2022.

At their only debate, last week, Pilip described herself as "pro-life" but also said she opposes a national ban and maintained that "I'm not going to force my own belief on any woman."

Suozzi is backed by abortion rights supporters.

Pilip has sought to center the race on local issues of public safety and immigration, arguing that she would be a vote for tougher restrictions on the southern border and address concerns over violent crime, which remain high despite dropping levels in New York.

She's also worked to tie Suozzi to Biden, underlining Suozzi's past voting record.

Why is this race happening?

The unusually timed race is taking place because former Rep. Santos was expelled from the House in a historic vote in the wake of various scandals over lies or fabrications about his background and after he was indicted on a slew of charges, including wire fraud and campaign finance violations. He has pleaded not guilty.

Santos hasn't been brought up extensively in the race, but outside allies of Suozzi, including the House Majority PAC -- House Democrats' main political group -- have highlighted past supportive comments of the disgraced former lawmaker by Pilip, whom Suozzi has labeled as a "Santos 2.0" because, he claims, she is "utterly unvetted" and "lying about her record."

The current special election is being held to see who will serve out the few months remaining in Santos' term -- it will not decide who will serve a full two-year term starting in January.

What are the stakes?

While Tuesday will see results from just one local congressional race, it has attracted outsized attention from both parties and has real political consequences for Washington.

In the short term, the election will impact House Republicans' wafer-thin majority, either adding a seat to their current three-vote cushion or helping Democrats cut into it further.

The narrow hold that the GOP has on the House has already been an obstacle to attempts at passing legislation.

Beyond that, operatives of both parties are looking to the race to discern what strategies work and don't work to inform their playbooks for later this year, including gauging Biden and former President Donald Trump's unpopularity, the issues of crime and immigration and where the winds are blowing in New York City's suburbs -- a region that alone could determine next year's House majority.

Still, Democrats are hoping to implement an entirely new congressional map across the whole state -- and given this race is just to finish Santos' term, the seat could ultimately look very different when the next term starts in 2025.

ABC News' Oren Oppenheim contributed to this report.

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