Just five months ago, the disgraced Hollywood mogul Harvey Weinstein was escorted in handcuffs past a phalanx of reporters and photographers and into the Manhattan Criminal Courts Building where a grand jury had voted to indict him, setting the stage for arguably the most important prosecution of the #MeToo era.

It was a moment of political redemption for the Manhattan district attorney, Cyrus R. Vance Jr., who had been fiercely criticized for not bringing charges against the producer in 2015. It also marked a cultural turning point for many women, a confirmation that Mr. Weinstein’s harassment of women went beyond boorish behavior: Prosecutors said he broke the law.

But now the case against Mr. Weinstein appears to be fraying. A detective failed to turn over important evidence to prosecutors. A judge dismissed part of the indictment. Evidence has emerged undermining the allegation of one of the accusers.

In addition, Mr. Vance’s assistants thought that once they filed charges, a flood of new complaints might lead to more victims being added to the case. It has not worked out that way.