Andrew P Bakaj took exception to claims by GOP congressman Jim Jordan, one of the president's most loyal allies, for claiming the anonymous official had had inappropriate communications with Democrats.
Mr Bakaj tweeted: "Congressman @Jim_Jordan - I AM TIRED OF YOU LYING IN A HOUSE COMMITTEE ROOM IN FRONT OF THE AMERICAN PEOPLE.
"My client hired ME - no one else in leading up to filing the disclosure with the ICIG. I have made that clear TIME AND TIME AGAIN - and you ignore the FACTS!"
He added: "And one more thing, @Jim_Jordan - NO ONE even within my firm - except for ME - knew the identity of my client until weeks, weeks later. Only I was involved - and there was NO "coordination" with anyone in Congress on anything involving the complaint.
"I see it simply troubles a number of individuals that the disclosure was made properly, through and through. That's why I was hired - because I know the Intelligence Community and the LAWFUL whistle-blowing process within the community."
Mr Jordan had been questioning Lt Col Alexander Vindman, a national security council expert who listened in to a controversial 25 July call between Mr Trump and Volodymyr Zelensky, the Ukrainian president. The Iraq veteran was so concerned by the content of the call, in which the US president appeared to be pressuring his counterpart to start investigations into Mr Trump's political opponents, that he raised it with an intelligence official.
The probe was originally launched after an anonymous official, thought to be a member of the CIA, made an official complaint about Mr Trump's behaviour.
The official has not been publicly identified and is entitled to remain anonymous. However, revelations that the whistleblower had reached out to the Intelligence Committee, chaired by Democrat Adam Schiff, for guidance on the complaint have been seized on by allies of Mr Trump as proof of a conspiracy.
In Tuesday's testimony Mr Schiff repeatedly admonished Republican members for apparently trying to unmask the whistleblower.
Congressman @Jim_Jordan - I AM TIRED OF YOU LYING IN A HOUSE COMMITTEE ROOM IN FRONT OF THE AMERICAN PEOPLE. My client hired ME - no one else in leading up to filing the disclosure with the ICIG. I have made that clear TIME AND TIME AGAIN - and you ignore the FACTS!— Andrew P. Bakaj (@AndrewBakaj)November 19, 2019
Mr Jordan said fears by Tim Morrison, a senior national security council member who was due to testify on Tuesday afternoon, that details of the call would leak had been proved correct. "Mr Morrison was right – the call leaks, the whistleblower goes to chairman Schiff's staff, then he runs off to the lawyer, the same lawyer who said in January of 2017 'the coup has started against President Trump'.
"The one thing the Democrats didn't count on ... was the president releasing the call transcript."
A tweet reading "the coup has started" was sent out by lawyer Mark Zaid, a lawyer Mr Bakaj says he added to the whistleblower team five weeks after the official came forward. Mr Zaid has said that his tweet has been taken out of context and actually referred to Mr Trump's sacking of Sally Yates as acting attorney-general.
Mr Bakaj tweeted: "I augmented my team with @MarkSZaidEsq WEEKS later. Why? Because I know him, I trust him, and he's an outstanding lawyer. Any insinuation otherwise is in an effort to deflect from the facts because facts can be tricky things."