President /www.huffingtonpost.com/topic/donald-trump"}}" data-beacon-parsed="true">Donald Trump’s former national security adviser, Michael Flynn, failed to heed warnings from the Pentagon about accepting foreign funds for a trip to Russia in 2015, the House Oversight and Government Reform Committee announced Thursday.

The Department of Defense sent classified documents to committee chairman Rep. Jason Chaffetz (R-Utah), said ranking member Rep. Elijah Cummings (D-Md.) at a news conference on Thursday. One of them, which is being prepared for public release, is a letter from the Defense Intelligence Agency to Flynn.

“This letter explicitly warned General Flynn, as he entered retirement, that the Constitution prohibited him from accepting any foreign government payments without advance permission,” Cummings said. “DIA did not locate any records of Lieutenant General Flynn seeking permission or approval for the receipt of money from a foreign source.”

But Flynn did accept the funds from Kremlin-backed news agency RT and failed to disclose them when he applied for a security clearance last year, Cummings and Chaffetz said Tuesday. He may have broken federal law.

Some of Flynn’s former staffers also warned him about accepting the $40,000 and participating in RT’s 10th anniversary gala. “Please, sir: don’t do this,” Simone Ledeen, who had worked with him in Afghanistan, said in an email at the time, according to The New Yorker. “It’s not just you. You’re a retired three-star general. It’s the Army. It’s all of the people who have been with you, all of these analysts known as ‘Flynn’s people.’”

A second letter revealed that “we have no evidence that he obtained permission from the Secretary of the Army and the Secretary of State to accept any foreign government payments, as required under the law,” Cummings said.

The White House never provided any documents related to what Flynn told the administration when he was vetted even though the committee formally requested it.

So they must have a “paper trail” of evidence, Cummings added. “I honestly do not understand why the White House is covering up for Michael Flynn. I watched [press secretary] Sean Spicer make all kinds of excuses about how hard it would be to comply with our requests. C’mon man.”

A third letter released shows the Pentagon’s inspector general announcement of yet another investigation of Flynn’s actions. Cummings said that Chaffetz, however, refused to have Flynn testify before their committee.

Committee members also expressed their support of the efforts to obtain documentation from the White House, according to a letter penned to Chaffetz on Thursday.

Trump named Flynn to be national security adviser in mid-November. Flynn resigned from the position in mid-February.

This article has been updated with more information about requests for documentation.