SAN JOSE — After losing a second ballot recount this week costing him nearly $15,000, Councilman Manh Nguyen filed a lawsuit to overturn the results of the June election that handed him a narrow defeat — a case experts say will be tough to win.

But the incumbent councilman, who’s been in office a little more than a year, is not giving up. His attorney claims the June 7 primary election was botched by the Santa Clara County Registrar of Voters and Nguyen should get a second bite at the apple.

Nguyen did not return calls Wednesday. He lost the election by 12 votes to challenger Lan Diep, an attorney who originally trailed Nguyen by 193 votes. Diep narrowed the gap as additional ballots were counted.

Two recounts of more than 17,000 ballots cast in the North San Jose district followed — one paid for by the county and the other by Nguyen — with each recount affirming Diep the winner.

But the number of total ballots tallied changed with each recount, said Nguyen’s attorney. That’s the backbone of the councilman’s legal case, led by Bradley W. Hertz of the Sutton Law Firm, who alleges those “inconsistencies” may have cost Nguyen his job. On Monday, Hertz filed a lawsuit challenging the contest in Santa Clara County Superior Court, asking that Nguyen be declared the winner, or that a judge void the June election and set a new one in November.

But the complaint was filed “pro per” — meaning Hertz won’t represent Nguyen in court and the councilman must represent himself. It also alleges eligible voters were “denied their right to vote” but doesn’t elaborate.

“Our allegations are that the election was mismanaged in such a way that the outcome is not as it purports to be,” Hertz said Wednesday. “Our first goal is to prove Manh Nguyen as the winner, but we won’t know that until we delve more deeply into evidence. At the very least, we think we’ll be able to prove so many problems and flaws, that no one should be declared the winner.”

Hertz alleges five people voted twice, a number of “duplicate” ballots weren’t linked to their originals, and elections officials didn’t properly initial ballots — a practice not required by law, but a “safeguard” enacted by the county.

Assistant Registrar of Voters Matt Moreles said those five voters turned in absentee ballots and still voted on Election Day — but weren’t given a provisional ballot.

“This wasn’t something specific to District 4 or even our county,” Moreles said. “Many other counties in the state reported this issue, mostly due to voter confusion.”

But Hertz can’t say if any of those alleged discrepancies would have put Nguyen ahead of Diep. And that’s what experts say makes this case difficult to prove.

“They can’t just say we have errors and we lost our confidence — that’s not going to work,” said Fredric Woocher of Los Angeles-based Strumwasser & Woocher, who specializes in election law. “Technical errors aren’t going to matter if you can’t prove it changes the results of the election. He has yet to show how any of these errors have resulted in him winning.”

Richard Hasen, a professor specializing in election law at UC Irvine School of Law, said successful election challenges are extraordinarily rare and showing variances between the vote tallies isn’t enough.

“There’s a high burden of proof in these cases because we don’t want courts to be lightly overturning the results of the election,” Hasen said.

Hasen and Woocher both agree Nguyen must prove that “illegal votes” were counted and that the errors were sufficient enough to change the election.

Diep, who squared off against Nguyen last year and lost by 13 votes, said the councilman should accept the results and “not hold the district and the city hostage to his ego.”

None of the errors outlined by Hertz “rise to the level of thwarting the will of the people,” Diep said, adding that he has confidence in the integrity of the process.

And while the legal battle rages on, political observers say the dragged-out process is costing Nguyen even more in the court of public opinion.

“If he loses the lawsuit, he simply looks like a sore loser,” said political consultant Richard Robinson. “At the end of the day, you need to shake hands, congratulate the victor and work for the benefit of your community.”

Contact Ramona Giwargis at 408-920-5705. Follow her at Twitter.com/ramonagiwargis.