Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa), with Sen. Dianne Feinstein (D-Calif.), prepares to open a meeting of his panel to consider a bipartisan effort to protect special counsel Robert S. Mueller III's job. (J. Scott Applewhite/AP)

Democrats are warning that the Senate Judiciary Committee chairman’s proposed changes to a bill to protect special counsels from undue firing would give the GOP the ability to tip off President Trump about developments in Robert S. Mueller III’s probe of him — the latest flash point on the legislation’s rocky road to a committee vote, expected Thursday.

Chairman Charles E. Grassley (R-Iowa) has been circulating a draft of his amendment, which he plans to offer Thursday as a stand-in for the special-counsel protection bill that Sens. Lindsey O. Graham (R-S.C.), Cory Booker (D-N.J.), Thom Tillis (R-N.C.) and Christopher A. Coons (D-Del.) unveiled two weeks ago after months of negotiations.

Grassley characterized the amendment as an improvement to the legislation, which has raised constitutional separation-of-powers concerns because it potentially subjects the president’s decision to fire a special counsel to a review by a panel of three federal judges. The amendment adds reporting requirements to Congress that Grassley believes would equip lawmakers to act to protect a special counsel — potentially by even starting impeachment proceedings — if the courts strike down the constitutionally controversial parts of the legislation.

But Democrats see a potential Trojan horse in those reporting requirements, which require special counsels such as Mueller to inform the House and Senate Judiciary Committee leaders “if there is any change made to the specific nature or scope of the investigation of the Special Counsel,” within 30 days of making that change.

Sen. Dianne Feinstein (Calif.), the panel’s ranking Democrat, told reporters Tuesday that if the amendment is adopted as written in the draft, she would oppose the special counsel bill, her office confirmed.

Once sensitive information about Mueller’s probe is in the hands of lawmakers, Democrats fear Trump’s allies on the Hill could pass the information on to the president and his lawyers, to keep the president and his affiliates a step ahead of Mueller’s probe. Even if information isn’t passed directly to the White House, Democratic aides complained, some lawmakers might try to exert political influence over the probe if they know in which direction it is heading.

According to a copy of the drafted obtained by The Washington Post, Grassley’s amendment would also require the special counsel to give lawmakers a specific argument about why they cannot publicize the information they receive if doing so would jeopardize national security, compromise some other, separate criminal investigation or proceeding, or otherwise violate laws. The amendment also stipulates that the special counsel must justify his or her probe to the attorney general for purposes of approving the budget every 90 days.

But where Democrats see room for political ma­nipu­la­tion, Republicans see a safeguard against it.

Grassley conceived of the amendment as a sort of backup plan for the compromise special counsel protection bill — which is preserved in its entirety as a part of his amendment. He, like several others, has raised concerns that the procedure for reviewing an order to fire a special counsel, which delays the firing for 10 days and guarantees an ousted counsel judicial review within 14 — might not stand up in court if challenged on constitutional grounds.

A Republican aide who spoke on the condition of anonymity to freely discuss the matter questioned why Democrats would want Congress to have less access to information about the status of a special counsel’s probe, if their objective was to defend the special counsel’s ability to do his work free from interference.

“We’re trying to contemplate these different scenarios to try to prevent tampering with an investigation,” the GOP aide said.

Grassley’s amendment also spells out the terms under which a special counsel may be appointed. Those sections are not expected to cause any dispute between the parties.

It is not clear whether the amendment will change before Grassley is expected to present it to the Judiciary Committee for its consideration. The authors of the special counsel bill are discussing the details of the proposed amendment with Grassley’s staff in the hope of working out a compromise.

The bill probably will need a strongly bipartisan endorsement from the Judiciary Committee if it is to stand a chance of being considered on the Senate floor; Majority Leader Mitch McConnell (R-Ky.) last week told Fox News he would refuse to bring it to a vote.

Tillis and other sponsors of the legislation said last week they were working to change McConnell’s mind.