Jurors in the perjury trial of Roger Clemens have endured six weeks of testimony from more than 30 witnesses, including former major league baseball players, a steroid dealer and even a housekeeper.

But as the trial enters its final stages, they have not heard from a critical set of witnesses who were present at the scene of the alleged crime, an ornate congressional hearing room where the legendary pitcher is accused of having committed perjury. In a twist that could occur only in Washington, Clemens’s alleged victims — the lawmakers themselves — elected not to testify.

That might change as early as Monday, when U.S. District Judge Reggie B. Walton hears arguments from Clemens’s attorneys, who are seeking to force Rep. Darrell Issa (R-Calif.) to take the witness stand.

Known on Capitol Hill for wielding his own subpoena power, Issa is fighting a subpoena from Clemens’s attorneys, who say that their client has a right to confront his accuser. House lawyers say Issa is too busy to appear in court and is shielded from doing so by a relatively obscure provision of the Constitution.

Legal experts are split in their opinions on how Walton might rule, but they mostly agree that the showdown highlights a central absurdity of the trial: Lawmakers sought the Justice Department investigation into Clemens’s testimony but won’t appear in court.

“Here you have federal prosecutors going out on a limb to help these guys, members of Congress,” said Roscoe Howard, a former U.S. attorney for the District. “It seems inherently unfair when lawmakers refer someone for prosecution and then don’t show up at a public trial to give their perspective or even tell why this case is as important as they say it is.”

Clemens, baseball’s most decorated pitcher, is charged with lying to the House Committee on Oversight and Government Reform in 2008, when he denied that he ever took performance-enhancing drugs. The hearing was nationally televised and dramatic: Clemens sat at the same witness table as his chief accuser, his former strength coach.

Under intense questioning from lawmakers that lasted more than four hours, the strength coach, Brian McNamee, alleged that he had injected the seven-time Cy Young Award winner with steroids or human growth hormone in 1998, 2000 and 2001. Just as assertively, Clemens denied the accusations, saying he had never taken any such substances.

Within days of the proceeding, the committee’s top Democrat and Republican sent a letter to then-Attorney General Michael B. Mukasey asking federal authorities to investigate whether Clemens “committed perjury and made knowingly false statements during” the hearing and to House investigators.

Federal agents quickly launched an investigation, and a grand jury in the District’s federal court indicted the right-handed pitcher in 2010 on charges of perjury, false statements and obstruction of Congress . The trial has been plodding along since April 16 — two jurors have been dismissed for sleeping — and prosecutors rested their case Tuesday. The defense, which is expected to include testimony from McNamee’s estranged wife and Clemens’s wife, could wrap up by Friday.

No testimony, no comment

To make their case, prosecutors must prove that Clemens lied and that those false statements were “material,” or important, to Congress’s work. But lawmakers on the committee have not testified to help prosecutors prove that element of the alleged offense. Rep. Henry A. Waxman (D-Calif.), then-chairman of the committee, refused to comment on why he did not take the stand, citing a judicial “gag” order. Issa, the current chairman, also declined to comment.

It is not known whether prosecutors asked Waxman or other members to testify, but the lawmakers have done so in the past. Two members of Congress — Lee H. Hamilton (D-Ind.) and Henry J. Hyde (R-Ill.) — willingly testified in John Poindexter’s Iran-contra case in 1990 — one for the prosecution, the other for the defense. Hamilton could not remember whether he was subpoenaed but said in an interview, “I felt it was my obligation to testify.”

Instead of making a legislator available to prosecutors and defense attorneys in the Clemens trial, the committee designated a former top staffer — Phil Barnett — to take the witness stand. Over 11 often-grueling hours on the witness stand, Barnett said the committee sought Clemens’s testimony because lawmakers wanted to gauge the accuracy of a 2007 report that found rampant steroid use in major league baseball. The former pitcher appeared voluntarily before the committee.

The report, by former senator George J. Mitchell (D-Maine), relied on McNamee’s accusations about Clemens and other ballplayers. When the report was made public and Clemens vehemently denied the allegations, committee members wanted to see whether they could trust the report’s conclusions and would need to take further action to reduce the use of performance-enhancing drugs in baseball, Barnett testified.

‘McCarthy era’

But not all members of Congress felt that way. At least one congressman called the hearing a “show trial,” and the Republican minority staff issued a lengthy and highly critical report about the allegations contained in the Mitchell report.

And then there is Issa, who ascended to chairman in 2011 after Republicans took control of the House. The California congressman had seemed perturbed that the committee was holding the hearing, saying it appeared too focused on alleged steroid use by an individual player.

“We’re not prosecutors, and we’re not supposed to worry about a former pusher and a former [alleged] user,” he said. “We’re supposed to be dealing with a whole industry that had a problem.”

He also described the hearings as a witch hunt. “We don’t really have a mandate to be looking at this,” he told New York’s Daily News. “To me, it smacks of the McCarthy era.” He later told the same newspaper that “this was all about entrapping Roger Clemens.”

For obvious reasons, Clemens’s attorneys would like to have Issa repeat those comments to the jury and allow the defense to attack the “materiality” of the charges. If the committee’s chairman thought the hearing was a farce, they argue, how can jurors convict someone of lying during the proceedings?

So they subpoenaed Issa. In lengthy legal filings, House lawyers argued that Issa is too busy to testify and is protected by the Constitution’s “Speech or Debate” clause, which they wrote “bars compelled testimony about legislative acts.”

Clemens’s legal team, led by attorneys Rusty Hardin and Michael Attanasio, argued that Clemens’s right to a fair trial trumps any such protections for lawmakers, especially when the testimony would allow them to undercut a key element of the case. Issa, who attended part of the House investigators’ deposition of Clemens, is “well positioned to opine about the legislative purpose of the questions to Mr. Clemens and the materiality of his answers to those questions,” the pitcher’s attorneys wrote. “And Chairman Issa’s numerous comments to the media leave no doubt that his testimony will be” helpful to Clemens’s defense.

Legal experts say Walton could rule either way but is more likely to side with House lawyers. Ruling in favor of Clemens would probably spark an emergency appeal that could further delay the trial. Such a ruling might also lead to other members of Congress being subpoenaed to offer their opinions — a kind of arms race of dueling lawmakers. “It could get messy,” said Stanley Brand, a D.C.-based litigator who is considered an expert on the Speech or Debate clause and who represented Major League Baseball during congressional hearings in 2005.

However, Brand said, Hardin has an excellent argument, especially because this case is not a typical one involving a lawmaker seeking protection from investigators.

“When Congress is the one pushing the button and the government is prosecuting you for not showing up or for lying, then it could be argued that members of Congress have waived all of their objections and privileges,” Brand said.

Staff researchers Magda Jean-Louis and Lucy Shackleford contributed to this report.