WASHINGTON — The Democratic-led House Intelligence Committee said on Thursday that it had issued two new subpoenas demanding that Michael T. Flynn, President Trump’s former national security adviser, and Rick Gates, a former top Trump campaign aide, provide testimony and documents related to their interactions with Russians and other foreign powers.
The subpoenas, dated Wednesday, are tied to the Intelligence Committee’s investigation of Russia’s attempts to influence the American political system and whether Russia or other foreign interests could have influence over Mr. Trump, his family or associates.
Mr. Flynn and Mr. Gates played key roles providing information and testimony to Robert S. Mueller III, the special counsel who investigated Russia’s 2016 election influence campaign, and could boost efforts by House Democrats to raise the profile of Mr. Mueller’s conclusions with the public if they cooperate.
Representative Adam B. Schiff of California, the Intelligence Committee’s chairman, said Thursday that the subpoenas were necessary because Mr. Flynn and Mr. Gates had so far refused to fully cooperate with the committee voluntarily.
“That’s simply unacceptable,” he said in a statement. “The American people, and the Congress, deserve to hear directly from these two critical witnesses. We hope these witnesses come to recognize their cooperation as being with the United States, not merely the Department of Justice.”
It is not a new story. Democrats have struggled since the release of Mr. Mueller’s report in April to kick-start their own investigations on many of the same topics he explored. The White House has strongly resisted cooperating and tried to block former Trump aides from sharing material or testifying on Capitol Hill.
Mr. Flynn, who served only briefly as national security adviser in the White House, pleaded guilty in late 2017 to lying to the F.B.I. about conversations during the presidential transition with the Russian ambassador.
Speaking with reporters Thursday morning, Mr. Schiff said there was “a waterfront of topics that we are concerned about with Flynn,” beginning with his conversations with the then-Russian ambassador, Sergey I. Kislyak, and his decision to lie about it later. He also listed Mr. Flynn’s lobbying work on behalf of the Turkish government, which has attracted the interest of federal prosecutors, and his role in a contested plan to build nuclear power plants throughout Saudi Arabia.
Mr. Gates, who was a longtime aide to the Trump campaign chairman, Paul Manafort, served as deputy campaign chairman and helped organize Mr. Trump’s inauguration. He pleaded guilty in early 2018 to financial fraud and lying to investigators and agreed to aide the special counsel’s work. Mr. Manafort is serving a seven and a half year sentence for crimes including tax evasion and bank fraud.
Mr. Gates also worked with Mr. Manafort to transfer political polling data to a business associate tied to Russian intelligence, Mr. Mueller found.
The letters accompanying the subpoenas ask Mr. Flynn and Mr. Gates to hand over documents by June 26 and to testify on July 10. Other details were less clear. The committee did not release a list of documents it had requested from the two men, or specify whether their testimony would be given in public or private.
In the letters, the committee urged the men to view cooperation with the committee as a continuation of their pledges to assist federal investigators.
“While the committee understands that your cooperation agreement with the Department of Justice only requires you to testify for the department, the committee is disappointed that you do not view your cooperation more broadly as an obligation to assist the United States of America, and not merely the Department of Justice,” Mr. Schiff wrote to Mr. Gates.