Cyrus Vance Jr. has served for less than two years in one of the highest-profile positions in U.S. law enforcement. (LUCAS JACKSON/REUTERS)

It’s a classic reversal of fortune.

The severe weakening of the sexual assault case against Dominique Strauss-Kahn has potentially restored the political hopes of the French presidential contender. But it has dealt a setback to the nascent career and political ambitions of Manhattan District Attorney Cyrus R. Vance Jr.

Vance has served for less than two years in one of the highest-profile positions in U.S. law enforcement. He is the son of Cyrus R. Vance Sr. — a Democratic lion and secretary of state under Jimmy Carter — and is the hand-picked successor of Robert Morgenthau, the legendary nine-term Manhattan district attorney.

But Friday, his office’s acknowledgment that it now questions the credibility of the chambermaid who accused Strauss-Kahn of sexual assault led to the Frenchman’s release from house arrest on his own recognizance.

The development caps a string of high-profile defeats for Vance.

“Major cases keep falling apart or acquittals occur where the public is hyped about the nature of the crime and the probability of conviction,” said Hank Sheinkopf, a Democratic consultant who has worked on several district attorney races but not on the 2009 election. “If Vance continues to lose cases where the electorate has an intense amount of information, he is going to have a problem. There are definitely people today thinking about whether Cy Vance should be challenged.”

At first, the Strauss-Kahn prosecution seemed an ideal opportunity for Vance to make a name for himself.

After filing the indictment, he spoke to reporters on the courthouse steps, characterizing the charges against Strauss-Kahn as “extremely serious” with evidence that “supports the commission of non-consensual forced sexual acts.”

This week, however, the most serious problems emerged with his own case. And for Vance, who took the district attorney’s office in a sharply contested election, this is not an isolated incident.

Detractors of Vance cite an exodus of experienced lawyers and growing tensions with Morgenthau as proof of his poor management skills. They point to a recent spate of courtroom losses as evidence of his tendency to overreach.

In May, a jury acquitted two police officers of rape charges made by Vance’s office in the officers’ handling of a drunk woman whom they helped into her apartment. The sensational nature of the case resulted in blanket tabloid coverage, as did the unexpected verdict. The officers were acquitted on all but official-misconduct charges.

In June, Vance argued that two men accused of plotting to blow up the largest synagogue in Manhattan had a “desire to commit violent jihad against Jewish Americans” and called it “not only an act of terrorism, but a hate crime.” His office failed to persuade a grand jury that the men intended to kill worshiping Jews, a hate crime that would have carried mandatory life sentences. Instead, his office settled for felony charges that carry a maximum of 25 years in prison.

On June 24, an Egyptian businessman pleaded down charges linked to his groping of a chambermaid in the Pierre hotel. He received a $250 fine and five days of community service.

Earlier this week, jurors acquitted two supervisors charged with negligently watching over construction of the former Deutsche Bank building in downtown Manhattan, leading to a 2007 fire that killed two firefighters. And two days before the Strauss-Kahn case faltered, the longtime chief of the Manhattan district attorney’s sex crimes unit, Lisa Friel, abruptly quit.

All those matters pale in comparison with the Strauss-Kahn case, in which Vance’s legal critics fault him with a rush to judgment. While New York law demands that prosecutors seek an indictment for such a crime in five or six days, Strauss-Kahn altered the legal calculus when he posted bail before the indictment.

The move gave prosecutors time to more thoroughly investigate the chambermaid’s assertions. But Vance sought to go to the grand jury quickly and pumped the case up in the media.

Vance declined to comment for this report, but his spokeswoman, Erin Duggan, said there was no rush. “This is how the criminal justice system works,” she said. She also objected to the notion that her boss was on a losing streak, saying that “a lot of homicides and sexual assaults never get a blip in the media.”

“We are not a baseball team. We don’t measure the work of the office on wins and losses, but on doing the right thing in every case,” she said, citing recent arrests in child pornography and drug-dealing cases.

Other defenders of Vance’s tactics came from unlikely quarters.

“It’s not fair to rush to judgments about him because he is taking over after a 30-plus-year reign,” said Leslie Crocker Snyder, a former New York judge who ran against Vance and had unsuccessfully sought to unseat Morgenthau several times.

Crocker Snyder said the instinct to “indict quickly” was “natural” given the high profile and serious nature of the alleged crime. But she said Vance was “fortunate” that Strauss-Kahn was “able to get out on bail, as high as it was. It could have been a much worse situation if he had been in jail like many people would have been.”

Vance grew up in New York and Washington and earned his law degree from Georgetown University in 1982. His father served in high government positions under Presidents John F. Kennedy and Lyndon B. Johnson before being named secretary of state under Carter.

In seeking the district attorney’s job in 2009, Vance explained that he had not wanted to pursue his father’s path, and sought to make his own way. He spent 16 years as a defense attorney in Seattle, suffering some other high-profile defeats, including one involving the case of teacher Mary Kay Letourneau. His defense of Joseph Meling, accused of sending cyanide-laced Sudafed capsules to kill his wife, ended in a conviction, as did the case of a businessman who strangled his Russian mail-order bride.

Vance returned to New York in 2004 as rumors spread that Morgenthau, then well into his 80s, was contemplating retirement. Five years later, when Morgenthau left office, he passed over likely heirs in the office to pick Vance, whom he thought would hold up his legacy. It hasn’t worked out that way; associates of the former district attorney have privately expressed that he is increasingly displeased with the performance of his successor.