(Reuters) - At a staff meeting this week, Manhattan District Attorney Cyrus Vance Jr. told prosecutors and investigators to ignore critics who blame the office for its recent high-profile setbacks, culminating in the teetering case against former IMF boss Dominique Strauss-Kahn. "I reject that criticism," he said, according to staff members at the meeting, which had been called to announce staff raises. "This office has never measured its success based on wins." But the reality is that Vance -- who, like most U.S. district attorneys is elected -- must balance his mandate as a dispassionate prosecutor with the politicking and attention to public perception inherent to elected office. That Vance understands the politics at play was made clear by an e-mail sent by his campaign team days after prosecutors disclosed that Strauss-Kahn's accuser, Nafissatou Diallo, an African immigrant working as a hotel maid, had changed her story about the alleged sexual assault and previously lied on her asylum application and her tax returns. Under a banner reading "Cy Vance for DA," the e-mail reprinted a New York Times opinion piece "The D.A. Did the Right Thing." The column by Joe Nocera praised Vance for turning over evidence that would surely make his prosecution more difficult. Beneath the article was a bright orange button labeled "Contribute." A spokesperson for Vance declined to comment on the e-mail. Observers say that if Vance is considering running for re-election in 2013, which such a message seems to suggest, he will be in for a fight. "I think he's going to have a serious challenge when he runs again," said Mitchell Moss, a professor at New York University and a former advisor to Mayor Michael Bloomberg. STREAM OF BAD NEWS The Strauss-Kahn roller-coaster is only the latest in a stream of bad news that has hurt Vance politically. In the last month, prosecutors lost cases against two New York police officers accused of assaulting a drunken woman and against contractors charged with negligence in a deadly fire at the former Deutsche Bank building. But neither of those cases carried the political freight that Strauss-Kahn's arrest does. Soon after news broke of Diallo's credibility issues, women's groups wrote a letter warning that prosecutors "must anticipate credibility problems" with sexual-assault victims. A coalition of advocates for immigrants and minority groups, led by state Senator Bill Perkins, also wrote a letter to Vance and held a news conference urging him not to drop the charges. "Not only have women generally been offended, but he's also managed to offend blacks," said Hank Sheinkopf, the veteran New York political strategist. "Is he done? The answer is no. Could he be? The answer is yes." Since women typically form a majority of voters in New York, they are a crucial demographic in city elections. Tuesday, Vance's office received a second postponement of the next hearing in the Strauss-Kahn case, originally scheduled for July 16. It is now scheduled for August 23. "I'd like to believe that the changing of the date was somewhat of a response to our earlier letter and public press conferences," Perkins said. Erin Duggan, the district attorney's spokeswoman, dismissed the suggestion that politics played a role in the postponements. "Cases are prosecuted on the basis of the facts and the law and nothing else," she said. 'THE GHOST OF MORGENTHAU' Vance, the son of former U.S. Secretary of State Cyrus Vance, spent much of his career as a defense lawyer in Seattle. He was largely unknown in New York before winning the endorsement of his predecessor, Robert Morgenthau. Succeeding Morgenthau, who built an international profile over more than three decades in office, may be Vance's biggest political liability. "The ghost of Morgenthau is hovering over him," said Arthur Greig, a lawyer and former counsel to the New York County Democratic Committee. In an interview, Morgenthau said he "ignored" the politics of high-profile cases and prosecuted "without fear or favor." He said the recent string of losses was meaningless, and that Vance would "do what he thinks is right." State Senator Thomas Duane, who endorsed Vance in 2009, said that while the district attorney was far from a natural politician, he was still new to the office and would survive. Experts also note that unseating a district attorney in any of New York City's five boroughs had proven all but impossible over the decades. Frank Hogan, the Manhattan district attorney before Morgenthau, held office for 32 years. Perhaps as important, Vance has more than two years to work on his image. "He looks lousy, no question, but will it have any electoral impact?" said Mickey Carroll, who runs the Quinnipiac University Polling Institute. "There will be a lot of water over the dam before anybody has to vote for or against him." (Reporting by Joseph Ax and Noeleen Walder; Editing by Jesse Wegman and Philip Barbara)