President Donald Trump‘s administration on Tuesday ordered a top diplomat who is a key witness in House Democrats’ impeachment inquiry not to appear before lawmakers for testimony.

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Alawyer for Gordon Sondland — the United States ambassador to the European Union — named Robert Luskin said the State Department directed Sondland to refuse to testify. Sondland exchanged text messages — which have now been published —  with several other diplomats about Trump’s repeated pleas to Ukraine’s government to probe Joe Biden. 

Trump explained the decision to block Sondland — a rich hotelier who donated to Trump’s 2016 campaign — from appearing before an interview with House lawmakers in a tweet Tuesday morning.

“I would love to send Ambassador Sondland, a really good man and great American, to testify,” Trump wrote, “but unfortunately he would be testifying before a totally compromised kangaroo court, where Republican’s rights have been taken away, and true facts are not allowed out for the public to see.”

The Trump administration’s move is likely to spur an aggressive from House Democratic committee leaders leading the impeachment inquiry. Democratic lawmakers have warned multiple times that the White House’s repeated efforts to stop witnesses from appearing before Congress for interviews could be construed as obstruction of justice. House Democrats could also possibly hold Sondland in contempt of Congress for refusing to testify.

The State Department’s move is likely to spur more subpoenas and other aggressive
It was reported last month that just days before Trump’s July 25 phone call with Ukraine’s president, the former leader’s administration had withheld $391 million dollars in military aid to the latter country. The transcript of the call also revealed Trump and Ukrainian President Volodymyr Zelensky discussed financial assistance to other nations, specifically European countries. Trump reportedly said he believed many of the continent’s nations — many of which are U.S. allies — were not contributing enough in military aid to Ukraine, which has been seeking funds to defend itself from a potential Russian incursion. According to The New York Times, Trump asked Sondland to take on a key role in relations between the U.S. and Ukraine, even though the country is not a member of the European Union.