Gordon Sondland has implicated a number of White House officials who were “in the loop” with Donald Trump's direction to withhold aid to Ukraine in an exchange for a meeting and a public statement announcing an investigation into the president’s political opponents.

The testimony came as Democrats were preparing to hold their fifth debate of 2020 in Atlanta, where they will undoubtedly be asked about the freshly sprung impeachment inquiry that has dominated headlines.

Mr Sondland, a US ambassador to the EU, affirmed that there was a so-called quid pro quo, dropping a bombshell testimony into another pivotal hearing in the House impeachment inquiry into the president’s alleged abuses of power in his dealings with Ukrainian president Volodymyr Zelensky.

According to his testimony, Mr Sondland worked under the president’s order to work with Rudy Giuliani “not because we liked it but because it was the only constructive path” to building a relationship with a vulnerable Ukraine. In emails and other conversations with US officials — including Vice President Mike Pence, Secretary of State Mike Pompeo and Energy Secretary Rick Perry — Mr Sondland established a clear link from the president, through Giuliani, and efforts to engage Ukraine with investigations into the 2016 election and Burisma.

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Mr Trump told reporters outside the White House that he barely knows Mr Sondland, who he previously called a "great American", and that he seems like a “nice guy".

The president read from a stack of papers in his hand, which included, in capital letters, his recollection of a conversation with Mr Sondland in which Trump said "I WANT NOTHING. I WANT NOTHING. I WANT NO QUID PRO QUO."

White House press secretary Stephanie Grisham said that "the US aid to Ukraine flowed, no investigation was launched, and President Trump has met and spoken with President Zelensky. Democrats keep chasing ghosts."

Mr Pence and Mr Perry also released statements during the hearing denying Mr Giuliani’s influence in their dealings with Ukraine. They’ve refused to testify in the impeachment probe.

Mr Trump also lashed out at his Democratic opponents conducting the House impeachment inquiry, mocked key witnesses giving testimony for their sartorial choices and denied that the onset of a heart attack was what prompted his sudden trip to hospital on Saturday.

"These people are sick. They’re sick. And the press really in this country is dangerous. We don’t have freedom of the press in this country. We have the opposite. We have a very corrupt media," the president ranted from the Cabinet Room of the White House on Tuesday.