An additional worry for Team Nunes: The clause does not protect activities that courts consider “political,” such as communicating with the executive branch on behalf of constituents, issuing a newsletter or news release or speaking outside of Congress. The most famous example involves Alaska Senator Mike Gravel and his staff, who were involved in the release and publication of the Pentagon Papers. The courts found that the speech or debate protections applied to Senator Gravel’s actions in entering the documents into the record of a subcommittee hearing, but did not apply to actions of the senator and his staff in arranging private publication following the hearing. The reason: The latter conduct was “in no way essential to the deliberations of the Senate.”

If a member or staff employee of the House Intelligence Committee engaged with the White House to stifle the special counsel inquiry, it would be difficult to see how such collaboration would be considered “essential to the deliberations” of the committee or the House. That would look a lot more like orchestrating than legislating. By contrast, constructive committee fact-finding with the agencies that were the subject of the Nunes memo — the F.B.I. and the Department of Justice — could well have headed off the distortions and omissions that have been identified upon the memo’s release. Mr. Nunes and his Republican colleagues refused even to accept a committee briefing on the memo from either agency.

This is not to suggest that piercing speech or debate immunity would be easy. Depending on the facts, the special counsel may determine that untangling which actions were protected and which were not is prohibitively challenging. But given the extraordinary nature of the circumstances here, no one should take the normal legislative immunity for granted.

That will be even more true if the Nunes memo serves as part of the pretext for Mr. Trump firing Mr. Rosenstein. Mr. Trump is already under obstruction investigation for firing the former F.B.I. director, James Comey, after Mr. Comey refused to pledge loyalty. Mr. Rosenstein rebuffed a similar demand. If he is terminated, that would be dispositive evidence of Mr. Trump’s pattern of obstruction of justice, and Mr. Nunes and his team will have helped make it possible. Whether or not all of that happens, if the House leadership cares about credible executive branch oversight they should demand from Mr. Nunes a thorough and prompt public response to Representative Quigley’s questions: What did Mr. Nunes’s office do, and when did they do it?