Ex-Rep. Mondaire Jones appears to have lost a battle for a liberal third-party line on Tuesday –  in a blow to the suburban Democrat’s comeback bid.

Jones appears to have lost the primary to run under the Working Families Party banner, an often crucial second ballot line that could spell the difference between victory and defeat for Democratic Party candidates in New York’s purple districts.

Jones was trailing unknown Anthony Frascone, who party officials claimed was put up to the race by Republican incumbent Rep. Mike Lawler’s camp in a bid to split the vote on the left.

“The GOP are a sad excuse for a political party if they can only win by stealing a ballot line,” fumed WFP spokesman Ravi Mangla.

The 17th Congressional District in the Hudson Valley takes in all of Rockland and Putnam counties, part of northern Westchester and Dutchess counties.

Frascone led Jones 185 votes to 153 votes in the WFP primary, according to unofficial tallies.

The WFP said Frascone, who resides in Congers in Rockland County, never came in for an endorsement interview and has no contact history with the party leaders.

Frascone has been a registered WFP member for a number of years.

But he also has a history of voting with the Independence and the Republican parties before joining the left-leaning WFP and he even ran for local office as an Independence Party member in 2011, Politico reported.

Frascone did not return a phone call for comment.

In the last presidential race in 2020, 13,000 people voted on the WFP line for Jones.

Jones had no immediate comment.

Lawler’s camp scoffed at claims that he and the GOP were behind the candidate who appeared to have defeated Jones in the primary.

“It sounds like Mondaire Jones is trying to point the finger at anyone other than himself for his primary loss last night. From the GOP to Jewish voters in Ramapo to progressive activists in district, no one is safe from his efforts to save face after an embarrassing loss,” said Lawler campaign spokesman Chris Russell.

“I hope this temper tantrum isn’t a preview of how he’ll react in November – if he can’t accept the results of an election now and concede, then how can anyone expect him to concede gracefully in November?” Russell quipped.

Rockland County Republican Party chairman Lawrence Garvey said he knows Frascone, but had nothing to do with him running against Jones in the WFP primary.

“For the Working Families Party to say the election was stolen by a member of their own party is the height of arrogance,” Garvey said.

Jones had a falling out with WFP leaders after he endorsed challenger George Latimer over the WFP-backed incumbent Rep. Jamaal Bowman in a Democratic primary in the neighboring 16th House District.

That district stretches through much of Westchester to Co-Op City in The Bronx. Latimer toppled Bowman in a landslide Tuesday night.

In 2022 after redistricting, Jones decided to abandon the Hudson Valley and instead run in the 10th Congressional District, covering downtown Manhattan and brownstone Brooklyn. Dan Goldman won the primary.

Jones now has moved back into the 17th CD, a move critics that saw critics blasting him as a “carpetbagger.”

“Mondaire Jones doesn’t know who he is, where he lives or what he stands for,” Garvey, the Rockland GOP leader, quipped.

Meanwhile, a similar situation happened in the Conservative Party primary in the 42nd state Senate district in the Hudson Valley.

Democratic Sen. James Skoufis, who is running for election to a fourth term, faces a rematch against Republican Dorey Houle, who he defeated narrowly by 1,400 votes in 2022.

The Conservative Party leadership in Orange County had cross-endorsed Houle, who ran on the party’s ballot line in 2022.

But Tim Mitts, a tax preparer who was convicted of filing fraudulent returns in Kentucky in 2008, won the primary.

Mitts in February changed his party registration from Repubilcan to Conservative.

Running on a second Conservative Party ballot line is often the difference between Republicans winning or losing in purple districts.