WASHINGTON (Reuters) - Congressional Democrats issued a subpoena for U.S. Energy Secretary Rick Perry on Thursday over any possible role he played in President Donald Trump’s effort to get Ukraine’s president to investigate a political rival.

“Recently, public reports have raised questions about any role you may have played in conveying or reinforcing the President’s stark message to the Ukrainian President,” the chairmen of three House of Representatives committees leading the probe wrote in a letter to Perry.

The letter from the chairmen of the Oversight, Intelligence and Foreign Affairs committees sought documents by Oct. 18, the latest effort from Democrats in Congress to secure evidence and testimony from the Trump administration.

The White House said on Tuesday it would refuse to cooperate with the congressional impeachment inquiry, hours after the administration abruptly blocked a key witness in the Ukraine scandal from testifying to congressional panels.

The Ukraine investigation has cast a pall over Trump’s campaign to win back the White House in 2020. A whistleblower complaint about a July 25 phone call in which the Republican president pressed his Ukrainian counterpart, Volodymyr Zelenskiy, to investigate his political rival, former Democratic Vice President Joe Biden, prompted the inquiry.