Special counsel Robert S. Mueller III is believed to be readying a report on his investigation of Russian interference in the 2016 election. (Yuri Gripas/Reuters)

The Democratic chairs of the six House committees investigating potential abuse of power by President Trump and his campaign’s business and alleged foreign ties will ask several executive branch agencies to preserve information they provided to special counsel Robert S. Mueller III as he investigated Russia’s interference in the 2016 election, according to congressional aides familiar with the plan.

The six House leaders and their Senate Democratic counterparts have signed a letter that will be sent to the Department of Justice, FBI and White House Counsel’s Office, among other agencies, shortly after Mueller submits his report to Attorney General William P. Barr, signaling the investigation’s conclusion.

It is an effort to ensure the agencies retain correspondence, memos, reports and other material should the committees request it, the aides said. They spoke on the condition of anonymity to discuss lawmakers’ planning.

House Democrats have struggled to obtain documents relevant to their investigations due to the administration’s aggressive posture toward the lower chamber, where Democrats hold the majority. The White House, for example, has refused to hand over materials sought in at least 15 letters written by congressional investigators on topics ranging from security clearances to the use of personal email by top Trump advisers, including the president’s daughter Ivanka Trump.

Beyond that, House Democratic chairmen say other agencies and department chiefs have rebuffed at least 30 inquiries on policy questions, according to a list provided to The Washington Post by senior Democrats overseeing the investigations. The administration’s strategy, Democrats argue, is an affront to Congress’ oversight responsibility.

On Friday, Trump dodged a question from a reporter about whether he was instructing his staff not to comply with congressional requests for information. “It’s just a continuation of the same witch hunt,” he said before leaving the White House for his Florida resort, Mar-a-Lago. “It’s just a continuation of the same nonsense. Everybody knows. They ought to go to work, get infrastructure done, and get a lot of other things done instead of wasting everybody’s time.”

Under the Presidential Records Act, all presidential records — except duplicates — are required to be preserved. Under the Federal Records Act, federal records are required to be preserved until the archivist of the United States permits their destruction. Unauthorized willful destruction is a crime. The letter reminds the agencies of these obligations and directs them to preserve the material, a senior congressional aide said.

The feud could wind up in court. House Democrats have discussed issuing subpoenas for the information, to compel the administration to cooperate. But even then, the White House could assert executive privilege, daring Democrats to sue.

The CIA, National Security Agency, Office of the Director of National Intelligence, and the Treasury and State departments also will receive preservation letters, congressional aides said.

House Democrats issued similar letters last year to most of the same agencies when Trump fired his first attorney general, Jeff Sessions.

Mueller was appointed in May 2017 by Deputy Attorney General Rod J. Rosenstein to investigate Russian interference in the 2016 election, potential obstruction of justice by the president and related matters.

The congressional investigations are wider ranging — to include looking at actions that may not constitute federal crimes.

“Our job is to protect the rule of law,” said House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.), one of the six chairmen signing the letter. Lawmakers are looking, for instance, at Trump’s attacks on the media, the federal judiciary and law enforcement agencies. “We have to look into questions of corruption, violations of the emoluments clause — it’s much broader than Mueller’s assignment.”

The other signatories are House Intelligence Committee Chairman Adam B. Schiff (D-Calif.); Oversight Committee Chairman Elijah E. Cummings (D-Md.); Foreign Affairs Chairman Eliot L. Engel (D-N.Y.); Ways and Means Chairman Richard E. Neal (D-Mass.); and Financial Services Chairman Maxine Waters (D-Calif.).

On the Senate side, signatories include: Judiciary Committee ranking Democrat Dianne Feinstein (Calif.); Intelligence Committee ranking Democrat Mark R. Warner (Va.) and committee member Ron Wyden (D-Ore.); Foreign Relations Committee ranking Democrat Robert Menendez (N.J.); and Banking Committee ranking Democrat Sherrod Brown (Ohio).