WASHINGTON — House Democrats just subpoenaed two men at the heart of Special Counsel Robert Mueller’s Russia investigation: former Trump campaign deputy chairman Rick Gates and Trump’s former National Security Advisor Michael Flynn.

The House Intelligence Committee is seeking testimony and documents from the one-time members of Trump’s inner circle who each became key cooperators in the Mueller probe after pleading guilty to charges of lying to investigators. The new subpoenas signal Democrats want to bring a sense of urgency to their hearings by calling in direct witnesses, rather than rely on outside legal experts as they have in televised hearings this week.

“Michael Flynn and Rick Gates were critical witnesses for Special Counsel Mueller’s investigation, but so far have refused to cooperate fully with Congress,” House Intelligence Committee chairman Rep. Adam Schiff said in an emailed statement Thursday. “That’s simply unacceptable.”

Both Gates and Flynn had secretive interactions with politically well-connected Russians during the months before Trump became president and are now awaiting sentencing in federal court. Gates spent years as the business partner and right-hand man of Paul Manafort, Trump’s former campaign chairman who was sentenced to roughly seven years in prison earlier this year for financial crimes and conspiracy.

The move comes as Democrats struggle to keep the public’s attention focused on Mueller’s findings following the release of his final report, which presented links between the Trump campaign and Russians and episodes of potential obstruction of justice without accusing Trump of committing a crime. The Dems are now attempting to call attention to the report’s most compromising details by calling forth witnesses and documents, despite resistance from the Trump administration.

Yet House Democrats have been spurned by Mueller, who has balked at requests to appear before Congress to explain his findings, and by some former administration officials who have refused to answer congressional subpoenas at the behest of the White House. As a result, the House held hearings this week on the “lessons” from the Mueller report that instead featured former FBI officials, cable news talking heads, and a historical figure from the 1970s Watergate scandal — without any direct link to Mueller.

The fresh subpoenas come just hours after Trump’s former White House communications director, Hope Hicks, agreed to speak behind closed doors to the House Judiciary Committee on the question of whether Trump attempted to obstruct the Russia probe this coming Wednesday. Democrats said a transcript of her remarks would be released afterward.

What they know

Neither Gates nor Flynn has ever provided a first-hand, public account of their own interactions with figures linked to Russia’s highest political circles during the campaign or presidential transition.

Gates and Manafort held a running conversation during the campaign with their longtime associate Konstantin Kilimnik, a Russian citizen the Mueller report said the FBI assesses “to have ties to Russian intelligence.” Manafort shared internal Trump campaign polling data with Kilimnik over a period of months and briefed him on “Manafort's strategy for winning Democratic votes in Midwestern states,” according to the report.

Kilimnik had previously served as an aide and translator for Manafort and Gates during the years when the three men worked together as advisors to Ukraine’s former pro-Russian president, Viktor Yanukovych. But Killimnik has publicly denied being a Russian spy.

The Mueller report also recounts how Flynn fielded phone calls with Russian Ambassador Sergei Kislyak in December 2016, weeks before Trump became president. In the calls, the two men discussed sanctions that the Obama administration levied against Russia for interference in the 2016 election — and Flynn told Kislyak that Moscow shouldn’t overreact and risk escalating the situation. Kislyak later told Flynn that Moscow took his advice, according to the report.

Letters sent to both Gates and Flynn demand they turn over documents by June 26 and appear before congress on July 10.