Declaring the probe ”constitutionally invalid”, the defiant eight-page letter to Democratic leaders accuses them of violating the US constitution and civil liberties.
It says they are attempting to overturn the results of the 2016 elections and “influence” the results of next year’s presidential race.
Signed by White House legal counsel Pat Cipollone, it adds that it would refuse to cooperate with the inquiry unless the US House of Representatives holds a formal vote to open an impeachment inquiry into Mr Trump.
It is addressed to the Democratic chairs of the House intelligence, foreign affairs and oversight committees, along with Nancy Pelosi, the house speaker, who launched the impeachment inquiry after accusations from a government whistleblower that Mr Trump sought Ukraine’s help in investigating Democratic rival Joe Biden.
She has repeatedly argued that what she launched is constitutional and that no House vote is necessary at this juncture.
However, the White House argued that the three other impeachment inquiries in US history against presidents Andrew Johnson, Richard Nixon and Bill Clinton all included House votes.
This should serve as precedent for Mr Trump’s impeachment, the letter says, adding that he has been denied basic due process rights, such as to cross-examine witnesses, call witnesses to testify, receive transcripts of testimony, and have access to evidence.
“All of this violates the constitution, the rule of law, and every past precedent,” it continues.
It said the US Supreme Court had recognised that due process protections apply to all congressional investigations.
Speaking as the letter was released, a senior administration official echoed this argument.
“Proceeding without a House vote is unprecedented in the history of our nation. In every prior occasion for a presidential impeachment inquiry there has been a vote of the House,” they said.
Details of the letter emerged shortly after the White House stopped a witness from testifying to Congress.
Gordon Sondland, the US ambassador to the European Union, did not give evidence after being ordered not to attend.
His attorney said that as a “sitting ambassador and current employee of state”, Mr Sondland had no choice but to follow the direction.
Mr Trump later tweeted: ”I would love to send Ambassador Sondland, a really good man and great American, to testify. But unfortunately he would be testifying before a totally compromised kangaroo court, where Republican’s rights have been taken away.”
Adam Schiff, the Democratic chair of the House intelligence committee told reporters that Mr Sondland’s no-show was ”strong evidence” of “obstruction of the constitutional functions of Congress, a coequal branch of government”.
He told reporters: “The American people have the right to know if the president is acting in their interests, in the nation’s interests with an eye toward our national security, and not in his narrow personal, political interests. By preventing us from hearing from this witness and obtaining these documents, the president and secretary of state are taking actions that prevent us from getting the facts needed to protect the nation’s security.”
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