WASHINGTON — With two short answers, Andy Pettitte called into question the validity of his testimony against Roger Clemens, part of a discouraging day for prosecutors in the retrial of the seven-time Cy Young Award winner.

After stumbling its way to a mistrial of Clemens last year, the government is struggling again in the retrial — to the point that the crux of Pettitte’s testimony might be tossed out. First, the exasperated judge criticized the questioning of Pettitte on Wednesday, then he ruled against prosecutors in another matter. Finally he cried out: “You’re taking positions that are totally absurd to me.”

Pettitte, Clemens’ longtime friend and former teammate, was on the stand for a second day in the trial that is to determine whether Clemens lied at a 2008 congressional deposition and hearing when he denied taking steroids and human growth hormone.