Mr. Nunes and his committee majority have demonstrated little regard for such niceties, and we fully expect them to weigh in on the side of the president, and against accountability. Should Mr. Mueller move to compel the president to testify by obtaining a grand jury subpoena, for example, look for them to back arguments circulated by Mr. Trump’s lawyers that the special counsel has not met the threshold for such a step. The fact that Mr. Mueller has accumulated compelling evidence of obstruction is unlikely to give the committee majority pause.

We also expect more overt attacks on Mr. Mueller himself, of the kind Representative Nunes has already launched against Obama-era officials for unmasking and the F.B.I. for the warrant against Mr. Page. Mr. Trump and his allies have already floated a long list of spurious assaults on Mr. Mueller and members of his team, smearing them with allegations of conflicts of interest, bias and abuse of their investigative powers. Now that the House Intelligence Committee majority has done its dirty work on the substance of the Mueller investigation, can picking up these themes to attack the special counsel himself be far behind?

We must in addition look for Representative Nunes and his ilk to back the president should he seek to install a crony in one of the positions within the Justice Department that oversees the Mueller investigation. Why should the president fire the special counsel outright, with the attendant fuss? Mr. Trump instead can try to throttle him by replacing Attorney General Jeff Sessions or his deputy, Rod Rosenstein, with a compliant soul who can slowly choke off Mr. Mueller by cutting his budget, trimming his staff or curtailing the scope of his review. In a week in which there has already been a major cabinet reshuffle, with the firings of Secretary of State Rex Tillerson and one of his top aides, Steve Goldstein, the possibility of such a move looms larger — and the likelihood of full-throated backing from Mr. Nunes and company, greater.

The damage the House majority can do here goes beyond mere cheerleading. When Mr. Nunes released his first memo, there were ominous rumblings that it was intended to target Mr. Rosenstein for his alleged role in FISA warrant abuses. When the memo fell flat, the rumors faded away. We would hardly be surprised to see a renewed effort against him — and his boss. Since Mr. Rosenstein oversees Mr. Mueller only because Mr. Sessions has a conflict (he worked on the Trump campaign), the replacement of either would serve Mr. Trump and Mr. Nunes’s malign purposes.

We predict that these and other forms of mischief will continue to flow from a committee majority run amok. Any oversight function that body might have provided as to Trump-Russia matters has been co-opted by the president, with the House Republicans even adopting his lie-ridden methodologies. A dangerous new era of alternative reality is advancing, and House Republicans are signaling that, like their president, they intend to ignore, bend or assail truth to fight the Mueller investigation (and presumably that of the Senate Intelligence Committee as well, should it reach inconvenient conclusions).

The special counsel must gird himself for this battle, and all of us must be ready to defend him. If Tuesday’s apparent victory by the upstart Conor Lamb in a deeply red congressional district in Pennsylvania is any indication, voters may ultimately relieve Mr. Nunes and company of their seats, or at least their power. In the meantime, Americans who are concerned about the integrity of our democracy must speak out against these intolerable efforts to undercut a vital investigation.