Manhattan better get used to Cyrus Vance.

Ken Thompson’s convincing primary victory over longtime Brooklyn District Attorney Charles J. Hynes on Tuesday stepped on a central tenet of district attorney elections in New York City: that incumbent prosecutors can serve as long as they like. That wisdom still holds in Manhattan, however, at least for four more years.

Manhattan District Attorney Cyrus Vance at a July press conference announcing a Mafia indictment. AP Photo/Bethan McKernan

Vance, the first-term Manhattan district attorney and successor to esteemed prosecutor Robert Morgenthau, doesn’t have an opponent in this year’s elections. Elected in 2009, Vance not only endured criticism early in his first term as Manhattan’s chief prosecutor after the troubled prosecutions of former International Monetary Fund head Dominique Strauss-Kahn and two New York City police officers accused of rape — he also began an aggressive fundraising campaign in the first half of 2011. Vance raised more than $800,000 and scared off any potential rivals.

“I don’t know the reason frankly,” said Leslie Crocker Snyder, a former Manhattan criminal court judge who lost to Vance during the Democratic primary in 2009, when asked why no one came forward to challenge Vance. “Maybe no one is interested in the job. Maybe no one has the money.”

The power of incumbency looms larger in district attorney elections than in every other elected office, and not just because it comes with no term limits. The phenomenon of eternal terms for prosecutors is, in fact, a national one.

A few years ago, Wake Forest law professor Ronald Wright studied about 10 years worth of prosecutor elections in 12 jurisdictions and determined that sitting prosecutors won 95 percent of the time when they run for re-election.

“It’s risky to go after the district attorney,” Wright said. “To think about the pool of people who were qualified for the job, they’re either district attorneys and you have to run against your boss, or they’re criminal defense attorneys.”

Meanwhile, many attorneys are motivated to contribute funds to support the incumbent’s reelection. “Every lawyer wants to feel that he or she is in good standing with the district attorney’s office,” Snyder said.

Vance’s campaign treasury held a $1.6 million balance as of July. A spokesman for Vance’s campaign did not respond to a request for comment for this story.

During this election cycle, Vance’s biggest financial backers have included investment banker Herbert A. Allen, Blackstone CEO Stephen A. Schwarzman and corporate litigator Marc E. Kasowitz, who contributed $56,993 in two separate transactions. The Vance campaign refunded a $25,000 contribution from Kasowitz last May, according tocampaign finance disclosures.

Lawyers who worked at Kasowitz’s firm supplied Vance with a steady stream of smaller contributions, as did lawyers fromMorgenthau’s law firm, Wachtell, Lipton, Rosen & Katz.

A small handful of criminal defense attorneys who occasionally spar with the Manhattan District Attorney’s office also pitched in. Ronald Fischetti, a veteran defense attorney who won an acquittal on a rape trial in Manhattan in 2010, contributed $2,500.

Robert Gottlieb, who two years ago asked the Manhattan District Attorney’s office to drop a murder case from 1998, donated $1,500 to Vance’s re-election. Gottlieb also served on Vance’s transition team. The district attorney’s office denied the request to drop the murder charges earlier this year.

Doug Muzzio, a political science professor at Baruch College, said Vance built up a substantial record after his initial stumbles — and proved he could raise money. Muzzio said he speculated the field of potential opponents simply thought they couldn’t beat him.

“It’s not only the record, but he proved to be a prodigious fundraiser,” Muzzio said. “So you’re running against someone’s record but someone who could also out-raise you. When you have both the money and what can be a convincing record, it’s tough to lose, particularly for a district attorney.”

Daniel L. Greenberg, the former president of the Legal Aid Society, said the failed prosecution of Strauss-Kahn may have served as fodder for a potential challenger had it occurred in an election year, instead of two years out.

Vance doesn’t seem to be going anywhere. But nor can he forever expect voters to have amnesia about missteps, if too many pile up. For Hynes, his nearly 24 years in office gave Thompson enough ammunition to wage to a successful campaign by focusing on a series of recent wrongful convictions and other scandals at the Brooklyn prosecutor’s office.

“When you’ve served as long as Hynes had, that’s the flip side,” Greenberg said.

Correction: An earlier version of this article misspelled the last name of Wake Forest law professor Ronald Wright.