House Republicans moved to pre-emptively kill any investigations against its members as it curtailed the power of an independent ethics office just as it was weighing whether to open inquiries into lawmakers who defied subpoenas issued by the House January 6 select committee last year.

The incoming Republican majority also paved the way for a new special subcommittee with a wide mandate to investigate the US justice department and intelligence agencies, which could include reviewing the criminal probes into Donald Trump and a Republican congressman caught up in the Capitol attack inquiry.

The measures took effect as House Republicans narrowly passed the new rules package that included the changes for the next Congress, 220-213, setting the stage for politically charged fights with the Biden administration over access to classified materials and details of criminal investigations.

Seeking to protect itself, the rules package first undercut the ability of the office of congressional ethics (OCE) to function, with changes that struck at its principal vulnerabilities to defang its investigative powers for at least the next two years, according to sources familiar with its operation.

The changes to the OCE are twofold: reintroducing term limits for members of the bipartisan board, which would force out three of four Democratic-appointed members, and restricting its ability to hire professional staff in the first 30 days of the new congressional session.

The issue with the changes, the Guardian previously reported, is that the OCE requires board approval to open new investigations, while new hires are typically approved by the board. The term limits would mean Democrats need to find new board members, which can take months – far longer than the 30 day hiring period.

In essence, the changes mean that by the time the OCE has a board, it may have run out of time to hire staff, leaving it with one counsel to do possible investigations into the new House speaker Kevin McCarthy and other Republican lawmakers who defied January 6 select committee subpoenas.

There would also only be that one counsel to investigate Republican congressman George Santos, who lied about his past during his election campaign; the OCE has the power to retrospectively examine violations of federal election law that arise during congressional election campaigns.

Once an OCE investigation is complete, the body can refer the matter to the full House ethics committee, which conducts its own inquiry. Crucially, however, even if the ethics committee dismisses a case, it is required to release the full OCE report, creating a deterrent for lawmakers.

Meanwhile, as House Republicans moved to shield themselves from potential ethics investigations, they expanded their own investigative ability through the adoption of the rules package that allows for the creation of the special subcommittee to probe the justice department and intelligence agencies.

The text of the resolution creating the subcommittee – scheduled for a vote on Tuesday – on “the weaponization of the federal government” authorizes it to investigate any part of the federal government, including “ongoing criminal investigations”, which Republicans have indicated could extend to probes against Trump.

The subcommittee will have subpoena power and receive materials provided to the House intelligence committee, meaning if the intelligence community were to ever give a briefing on the classified documents the FBI seized from Trump’s Mar-a-Lago resort, the panel would obtain that, too.

And while the subcommittee will have its own chairman, it remains part of the House judiciary committee led by Jim Jordan, who maintains the ability to issue subpoenas on behalf of the panel and ultimately inherit all of its materials whenever it is dissolved, according to the resolution text.

Whether Jordan and the special subcommittee will ever receive materials from the justice department about active criminal investigations in practice remains unclear.

The department has long refused to provide to Congress confidential grand jury material, information that could compromise criminal investigations, and deliberative communications such as internal prosecution memos because of the risk of political interference in charging decisions.

As the department explained in a letter to the House rules committee chair John Linder in 2000, its position has also been upheld by the supreme court in Nixon v United States (1974) that recognized making such materials public could have an improper “chilling effect”.

Particularly with respect to cases involving Trump, current and former officials said the current justice department would likely adopt the same position as the Linder letter, which concluded: “The Department’s longstanding policy is to decline to provide congressional committees with access to open law enforcement files.”