In Gravel v. United States that same year, the court reviewed an investigation by a grand jury into the release and publication in the Congressional Record of the Pentagon Papers. In that case, the justices found that the clause protection also covers an aide to a senator “with respect to legislative acts.” Therefore, when a congressional aide engages in conduct relevant to “committee reports, resolutions and the act of voting,” the aide is also protected from any inquiry.

Mr. Collins’s claim was based on a 2007 decision by the federal appeals court in Washington involving a search by F.B.I. agents of the office of Representative William J. Jefferson of Louisiana for possible bribery. The appeals court found that information in a congressional office could not be inspected or seized by the executive branch because the clause prohibits any inquiry into the materials in a congressional office.

But the federal appeals courts for the Ninth and Third Circuits, in other cases involving members of Congress, did not read the clause as protecting all information of congressional staff members.

Following the lead of those two rulings, Judge Broderick found that the Constitution does not provide absolute protection from a criminal inquiry. He concluded that any questioning of Mr. Collins’s current or former staff members about Innate Immunotherapeutics did not involve legislative activity. Moreover, Judge Broderick noted that Mr. Collins’s attorney had conceded that a superseding indictment issued by a grand jury was designed to avoid any “speech or debate” evidence and did not contain anything protected by the constitutional protection for legislators. That meant any appeal of the ruling faced very long odds of succeeding.

Because there was nothing related to legislative activity in the charges, Judge Broderick’s decision not to dismiss the indictment was fairly straightforward.

He did decide to prohibit the government from using an interview Mr. Collins had with the Office of Congressional Ethics about his conduct related to the failed drug trial. The judge found that excluding this evidence might avoid a possible appeal by Mr. Collins.

The ruling most likely provided Mr. Collins little room to win on appeal.

The “speech or debate” clause, though, is one of the few constitutional protections that can be appealed immediately. In United States v. Helstoski in 1979, the Supreme Court concluded that a member of Congress can immediately appeal a denial of a motion to dismiss on those grounds because there is no way to protect the member from enduring a criminal prosecution that incorporated evidence of legislative activity.

Mr. Collins could have appealed Judge Broderick’s decision to the United States Court of Appeals for the Second Circuit in Manhattan and then to the Supreme Court. Now that he has pleaded guilty, federal guidelines recommend a sentence of 15 to 21 months because the amount of the losses avoided by Mr. Collins’s son and Mr. Zarsky exceeded $550,000. Prosecutors are recommending a sentence of 46 to 57 months because he also lied to the F.B.I.