Updated on June 9 at 4:24 p.m. ET

One of the Senate’s longest-serving Republicans is calling out the Trump administration for adopting a policy that would allow the government to ignore most congressional demands for federal records.

Senator Charles Grassley of Iowa, the chairman of the Judiciary Committee, on Friday sent a letter to President Trump in which he attacked as “nonsense” a formal legal finding by the Department of Justice that federal departments and agencies are only obligated to respond to congressional oversight requests that come from committee chairmen. The policy means that Democrats, who are the minority party in the House and Senate and thus have no chairmanships, would have virtually no way of compelling information from the Trump administration unless they persuaded a powerful Republican to sign on to their requests.

“I know from experience that a partisan response to oversight only discourages
bipartisanship, decreases transparency, and diminishes the crucial role of the American people’s elected representatives,” Grassley wrote in his letter to the president. “Oversight brings transparency, and transparency brings accountability. And, the opposite is true. Shutting down oversight requests doesn’t drain the swamp, Mr. President. It floods the swamp.”

Grassley’s decision to challenge the Trump administration on congressional oversight is significant not just because he is a Republican, but because as a committee chairmen he would not be affected by the restrictive policy. As he noted in his letter, limiting oversight demands to committee chairmen could shut out many Republicans, although they would have an easier time running their requests through their more senior colleagues. “It obstructs what ought to be the natural flow of information between agencies and the committees, which frustrates the Constitutional function of legislating,” Grassley wrote.

The White House solicited an opinion from the Justice Department’s Office of Legal Counsel, which determined that only chairmen are vested with Congress’s formal power of oversight over the executive branch—a far narrower interpretation of the law than the Obama administration used. “Individual members who have not been authorized to conduct oversight are entitled to no more than ‘the voluntary cooperation of agency officials or private persons,’” the OLC opinion stated.

Democrats assailed the finding as a legal justification for stonewalling; House Minority Leader Nancy Pelosi accused the White House of “an attempted gag order” targeting Democrats who have seen the administration ignore more than 200 requests for documents in the first months of the Trump administration. In a rare departure from the partisan norm, Grassley sided with them. His seven-page letter to the president denounced the OLC’s opinion point by point and accused the office of “a shocking lack of professionalism and objectivity.”

It falsely asserts that only requests from committees or their chairs are ‘constitutionally authorized,’ and relegates requests from non-Chairmen to the position of ‘non-oversight’ inquiries— whatever that means.

This is nonsense.

First elected to the Senate in 1980, Grassley has generally been an ally of Trump’s, although he occasionally tries to get the president’s attention through his active and often entertaining Twitter feed. He’s long been a stickler for Congress’s oversight prerogative and frequently jousted with the Obama administration.

Grassley also has first-hand knowledge of how even a single member of the minority party can leverage his position. In 2011, before he became a chairman, he wrote a letter to the Obama administration seeking a response to the account of a whistleblower who claimed that firearms lost in the Justice Department’s Operation Fast and Furious had been used in the murder of a federal border patrol agent named Brian Terry. The letter that the department wrote in reply turned out to be inaccurate, deepening a scandal that prompted the Republican-led House to cite then-Attorney General Eric Holder for contempt of Congress.

Just this week, Grassley testified about the case before the House Oversight Committee and urged fellow lawmakers to pass legislation that would strengthen Congress’s ability to compel documents and information from the executive branch.

“I urge you to take off your partisan hats for a moment,” he said at the hearing. “Imagine if the shoe were on the other foot. This case has broad implications for the ability of the elected representatives of the American people to do our constitutional duty to act as a check on the executive branch. Clearly, Congress needs to do something.”

Senator Charles Schumer, the Democratic minority leader, thanked Grassley for his letter in a statement Friday. “We hope other Republican chairmen will follow Chairman Grassley’s lead  in demanding the administration withdraw this misguided memo,” he said. “This is the same standard they themselves set when they were in the minority."

The White House did not immediately respond to a request for comment on Grassley’s letter.