Former federal prosecutor and current CNN legal analyst Renato Mariotti urged House Democrats not get bogged down on the administration obstructing the process.
It lists examples, including that the president has been denied basic rights, such as the right to cross-examine witnesses and to have access to evidence.
The White House has notified the House that the Trump administration will not participate in what it is calling Democrats' "illegitimate" impeachment probe. The White House letter is only the latest attempt to cover up his betrayal of our democracy, and to insist that the President is above the law.
Cipollone also accused Congress of threatening executive branch officials with punishment for exercising "fundamental constitutional rights and prerogatives". The American people have already heard the President's own words - 'do us a favor, though.' The President's actions threaten our national security, violate our Constitution and undermine the integrity of our elections.
"The Whistleblower has ties to one of my DEMOCRAT OPPONENTS", he wrote.
Sondland replied: "Bill, I believe you are incorrect about President Trump's intentions".
A characteristically sarcastic George Conway, husband to White House counselor Kellyanne Conway, was unsurprised by the news that Sondland would not be testifying, tweeting: "But we were all so looking forward to his testimony about the world's most flawless presidential phone call".
Sondland - a Trump donor who started his diplomatic role in July - said he hoped "the issues raised by the State Department that preclude his testimony will be resolved promptly". They say they'll subpoena the ambassador for his testimony and communications on his personal devices that have not been turned over. President Trump was at 52% approval, 47% disapproval, among likely voters.
House Speaker Nancy Pelosi on Tuesday said President Trump is "obstructing Congress from getting the facts" it needs in the impeachment inquiry after his administration blocked a United States diplomat from testifying before three committees. Previous witnesses have been career officials, including the former US special envoy for Ukraine, Kurt Volker, and Michael Atkinson, the inspector general of the US Intelligence Community.
"As I said on the phone, I think it's insane to withhold assistance for help with a political campaign", Taylor wrote in a message on September 9.
The letter states that for these reasons, the White House won't comply with the demands of House lawmakers.