Democratic Nassau County executive candidate George Maragos has loaned his past three campaigns a combined $3.1 million — a tactic that candidates use often to boost the legitimacy of their campaigns to attract outside donors.

But state and federal campaign finance records show Maragos, who made millions of dollars at his private technology firm, repaid himself more than 90 percent — $2.89 million — after his two successful campaigns for county comptroller and a failed U.S. Senate run in 2012.

The loans appear to have had a minimal effect. They failed to spark an influx of big contributions, and Maragos was unable to drive rivals from the race for Senate.

He raised only $57,000 in the five months after loaning $1 million to his 2013 re-election campaign for comptroller. And he collected only $76,000 in donations after loaning his Senate campaign $1.9 million.

Maragos, who switched his party affiliation from Republican to Democratic last year, is challenging Legis. Laura Curran (D-Baldwin) in a September county executive primary.

Last July, Maragos loaned his county executive campaign $1 million, and made another $450,000 loan in January. It’s unclear how much of that money has been spent, as candidates do not report their fundraising and expenses until July 17.

The practice of candidates making loans to their campaigns, only to repay the money, is legal. But campaign finance experts say the tactic can give an unfair advantage to wealthy candidates who try to use loans to persuade prospective donors to take their campaigns seriously. The law puts no limits on the total loan amounts.

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“People like to give to a winner and one way to show you are a winner is the amount of money in your campaign account,” said Ian Vandewalker, senior counsel for the Democracy Program at the Brennan Center for Justice at NYU School of Law, a nonpartisan law and policy institute.

“Lending money to your own campaign lets you create a war chest that might or might not scare off potential opponents without having to raise the money from donors,” said Michael Malbin, executive director of the Campaign Finance Institute, a nonpartisan research group in Washington.

Maragos, who declined to be interviewed for this story, issued a statement defending the loans as proof of his political independence.

“I funded my previous campaigns with all the resources needed without relying on special interest money,” Maragos said. “I intend to spend what is necessary to win without wasting money, while maintaining my independence.”

In July 2009, during his first run for Nassau comptroller, Maragos loaned his campaign $200,000 but failed to attract any outside contributions, state campaign finance records show.

Maragos, along with GOP county executive candidate Edward Mangano, scored an upset win, and after Election Day Maragos’ campaign repaid him nearly $73,000, records show. Maragos was the lone comptroller candidate.

The following year, Maragos sought the Republican nomination for U.S. Senate to challenge Democrat Sen. Chuck Schumer (D-N.Y.), but was not selected at the party’s convention. Maragos raised less than $13,000 and made no loans to his campaign.

In 2012, Maragos sought the GOP nomination against Sen. Kirsten Gillibrand (D-N.Y.). State Republican leaders spread their endorsement among Maragos, then-Rep. Bob Turner of Queens, and attorney Wendy Long.

Maragos lent his campaign $1.94 million but with poor name recognition outside Nassau, finished third in the June GOP primary. Maragos refunded himself $1.84 million and later paid a $5,000 fine after the Federal Election Commission found he had misreported details of the loans.

In his 2013 re-election campaign for comptroller, Maragos loaned his campaign just over $1,001,000. The campaign repaid Maragos $984,000 after he defeated Democrat Howard Weitzman, a former Nassau comptroller, in a rematch of their 2009 contest.

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Michael Dawidziak, a Bohemia political consultant who works primarily with Republicans, said experienced politicians understand that loans are a political tactic meant to bluff opponents. Candidates who are serious about using their own money, he said, make direct contributions to their campaigns, which are not refundable.

Republican Michael Bloomberg gave his campaigns a total of $250 million for his three successful runs for New York City mayor. Democrat Jon Corzine spent $130 million of his own money in his successful race for U.S. Senate in 2000, and two races for New Jersey governor, one of which was unsuccessful.

“No serious candidate should ever be scared off because of a personal loan,” Dawidziak said. “If a candidate really believes in himself, make it a direct contribution.”