What’s happened in the impeachment inquiry overnight, and what’s next

The release of the letter followed the Trump administration's order blocking Gordon Sondland - the USA ambassador to the European Union - from testifying before Congress.

The White House will not participate in Congress' ongoing impeachment inquiry, it said Tuesday, stepping up a political and legal standoff between the executive and legislative branches of government.

White House press secretary Stephanie Grisham said in a statement: "The President has done nothing wrong, and the Democrats know it". In a memo reviewed by the New York Times, the whistleblower wrote that a White House official who listened to President Trump's July 25 phone call with Ukraine's president found the conversation "crazy" and "frightening".

"The Whistleblower has ties to one of my DEMOCRAT OPPONENTS", he wrote.

"You have denied the President the right to cross-examine witnesses to call witnesses, to receive transcripts of testimony, to have access to evidence, to have counsel present, and many other basic rights guaranteed to all Americans".

"You have conducted your proceedings in secret".

The Whistleblower Protection Act of 1989, 5 U.S.C. 2302 (b)(8)-(9), Pub.L. 101-12 as amended, is a United States federal law that protects federal whistleblowers who work for the government and report the possible existence of an activity constituting a violation of law, rules, or regulations, or mismanagement, gross waste of funds, abuse of authority or a substantial and specific danger to public health and safety.

"President Trump and his administration reject your baseless, unconstitutional efforts to overturn the democratic process", the eight-page letter read. President Trump was at 52% approval, 47% disapproval, among likely voters.

"Your unprecedented actions have left the President with no choice". 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.

"The President has a country to lead". The transcript shows Trump asking Zelenskiy for a favor and to investigate the Bidens.

Moreover, Cipollone argued that because there has been no formal vote to begin an impeachment inquiry, there is no official process underway and accordingly the administration is not required to comply.

The impeachment inquiry is focused on a whistle-blower's allegations that Trump used almost $400m in USA military aid to secure a promise from Ukraine's president to investigate Biden, a leading candidate for the 2020 Democratic presidential nomination, and his son.

Joe Biden's son Hunter sat on the board of Ukrainian natural gas company Burisma Holdings from 2014 to early 2019.