Rep. Marcus Molinaro of New York, a Republican in a swing congressional district, lost his reelection late Tuesday night to Democrat Josh Riley.

The election in the state’s 19th District was called by The Associated Press at 1:20 a.m. with Mr. Riley leading Mr. Molinaro 50.9% to 49.1%, with 95% of the votes tallied.

The rematch between Mr. Molinaro and Mr. Riley, after the Republican won by less than 4,500 votes in 2022, was a nasty horse race in the district, which stretches from Ithaca to the Catskill Mountains.  

In the closing weeks of this election, with the nonpartisan Cook Political Report rating NY-19 as a “toss up,” both campaigns spent millions of dollars, making it the state’s most expensive this cycle.

Mr. Molinaro, a political veteran who was elected mayor of Tivoli at age 19 and worked his way up the state GOP ranks, served in the Dutchess County Legislature before moving to the state assembly and later serving as county executive.

Four years after a failed gubernatorial bid against then-Gov. Andrew Cuomo, Mr. Molinaro was elected to Congress with several other freshmen Republicans from New York when the GOP recaptured the House from the Democrats.

Mr. Riley was born and raised in the upstate New York town of Endicott and joined a private legal practice after graduating from Harvard Law School.  

He began his career in government and politics when he started working as a policy analyst for the Department of Labor, and later as a staff assistant to former New York Democratic Rep. Maurice Hinchey.

He went on to work as general counsel to former Democratic Sen. Al Franken of Minnesota.

Both candidates sparred over the immigration issue, with Mr. Riley criticizing his own party for being “too slow to act on the border problem,” WSKG reported.

Mr. Riley supports more border agents in some regions and a “surge in immigration judges.”

During their Oct. 10 debate, Mr. Riley said, “Number one, secure the damn border. Send the technology. Get it off the shelves. Go do your job. Pay for the technology to go to the border to detect the fentanyl. Pay for it. Get it done. Stop the fentanyl from coming in.”

Mr. Molinaro, however, went after Mr. Riley for backing Democrats’ immigration stances and blamed Democrats’ border policies for the state’s violent crime and the problems downstate in New York City with its migrant crisis.

“I voted for the strictest border security policy in generations, and [President Biden] chose not to negotiate, not to engage, and instead turn his back,” Mr. Molinaro said during the debate.

Mr. Riley attacked Mr. Molinaro for voting to make it more difficult to get an abortion. He accused him of wanting to vote for a federal abortion ban, which Mr. Molinaro denied.

“The decision … should be left to a woman and a physician, not Washington … I oppose a national ban, and I remain committed to opposing a national ban,” Mr. Molinaro said.