WASHINGTON — Legislation designed to protect special counsel Robert Mueller from a sudden firing by the president is expected to get a committee vote before the end of the month, but its path forward is difficult, as partisan disagreements over the bill are already surfacing.

Senate Judiciary Chairman Chuck Grassley, R-Iowa, said Thursday that the committee is expected to vote April 26 on the legislation, introduced this week as President Donald Trump escalated his criticism of the special counsel. Grassley has not endorsed the bill, and said he has concerns that it is unconstitutional. But he said at an unrelated committee hearing that he believes the full committee should vote on it.

The legislation introduced by Republicans Thom Tillis of North Carolina and Lindsey Graham of South Carolina and Democrats Chris Coons of Delaware and Cory Booker of New Jersey — all members of the Judiciary panel — would write into law the existing Justice Department regulations that say a special counsel can only be fired for good cause and by a senior Justice Department official. It would also give any special counsel a 10-day window to seek expedited judicial review of a firing.

The bill’s bipartisan introduction signals escalating worries in Congress as Trump has fumed about Mueller’s Russia investigation and publicly decried an FBI raid of the office of his personal attorney, Michael Cohen, calling it “an attack on our country.”

Despite congressional concerns, the legislation faces several roadblocks.

Grassley indicated that some Republicans on the committee oppose it, and Senate Majority Leader Mitch McConnell, R-Ky., has shown little interest, saying earlier this week that he doesn’t think Mueller will be fired. Democrats have already said they are wary of a still-unseen amendment that Grassley plans to offer to the bill.

California Sen. Dianne Feinstein, the top Democrat on the Judiciary panel, said in a statement that she was concerned the amendment “could undermine the investigation.”

In prepared remarks issued at the beginning of a hearing Thursday, Grassley said the amendment would require the attorney general to give a detailed report to Congress “justifying significant decisions involving the special counsel, including the firing of the special counsel.”