The White House on Tuesday rejected an impeachment inquiry launched by Democrats in the House of Representatives as "constitutionally invalid" and said it would refuse to cooperate with the probe absent a vote of the full House.
An eight-page letter signed by White House counsel Pat Cipollone was sent to House Speaker Nancy Pelosi, the top US Democrat, and the Democratic chairs of the House intelligence, foreign affairs and oversight committees.
Pelosi argues the impeachment inquiry she launched is constitutional and that no House vote is necessary at this juncture.
The inquiry was started based on accusations from a government whistleblower that President Donald Trump sought Ukraine's help in investigating Democratic rival Joe Biden.
The White House argued that the three other impeachment inquiries in American history, against presidents Andrew Johnson, Richard Nixon and Bill Clinton, all included House votes, and that this should serve as precedent for the impeachment of President Donald Trump.
"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," said a senior administration official, speaking as the letter was released.
The letter said Trump 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," the letter said.
It said the Supreme Court has recognized that due process protections apply to all congressional investigations.
The letter was the result of an intense behind-the-scenes effort in recent days by White House lawyers to respond to the Democrats' impeachment bid.
One concern the White House has involves the whistleblower. House Democrats are working to protect the identity of the person who has accused Trump of impropriety in his dealings with Ukraine.
"There shouldn't be a situation where you can have a primary witness, an accuser in an impeachment inquiry, and the president never able to know who the accuser is and never able to cross examine him," said the senior administration official.
Trump has called the inquiry a partisan "witch hunt," and released a summary transcript of his July 25 phone call with Ukraine President Volodymyr Zelenskiy in a bid at damage control.
The letter argues - a contention denied by the Democrats - that the impeachment effort is simply aimed at reversing the result of the 2016 presidential election and influencing the 2020 election.
"The decision as to who will be elected president in 2020 should rest with the people of the United States, exactly where the Constitution places it," said the letter.