Sacked FBI boss James Comey’s evidence that he was pressured by Donald Trump to back off an investigation into links with the Russian administration, confirms the President should be impeached, a legal expert says.

US-based lawyer and legal analyst Jeffrey Toobin told CNN Mr Comey’s testimony of “very concerning”, “very awkward” and “inappropriate” conversations in which Donald Trump sought to influence the inquiry constituted an obstruction of justice – strengthening the case for impeachment.

“Let’s just keep this in perspective,” Mr Toobin told CNN.

“There is a criminal investigation going on of one of the President’s top associates, his former national security adviser [Michael Flynn], one of the most … handful of most important people in the government.

“He gets fired. He’s under criminal investigation and the President brings in the FBI director [James Comey] and says, ‘Please stop your investigation’.

“If that isn’t obstruction of justice, I don’t know what is.”

In written testimony on Wednesday, Mr Comey said Mr Trump told him at a meeting in the White House in February: ” ‘I hope you can see your way clear to letting this go, to letting Flynn go’.

” ‘He is a good guy. I hope you can let this go’,” Mr Comey’s written submission says.

“I replied only that ‘he is a good guy.’ (In fact, I had a positive experience dealing with Mike Flynn when he was a colleague as Director of the Defense Intelligence Agency at the beginning of my term at FBI.) I did not say I would ‘let this go’.”

Mr Comey, who was sensationally and controversially fired by Mr Trump in May, said he held nine separate face-to-face and phone conversations with the president.

He wrote that Mr Trump phoned him on March 30 and asked what “we could do to lift the cloud” of the FBI’s Russia investigation.

Meanwhile, two Democrat congressmen are drafting articles of impeachment against Mr Trump, the UK’s Independent newspaper has reported.

Al Green, of Texas, and Brad Sherman, of California, announced what the paper couched as a “long-shot bid” to impeach on the basis that firing Mr Comey was an obstruction of justice.

“The question really is whether the president can obstruct justice with impunity,” Mr Green told a press conference.

“We live in a country where no congressmen, no senator, and not even the president of the United States of America is above the law.”

However, with the Republicans in control of the House of Representatives, which would initiate proceedings, the bid seems more symbolic than feasible.

Researcher at the University of Melbourne’s School of Government, James Cahill, would not be drawn on the potential for impeachment, but said Mr Comey’s statement was still hugely significant.

Mr Cahill said his statement confirmed the many leaks over recent weeks, which the Trump administration had sought to play down as “fake news”.

“What’s significant is that not only did he (Mr Comey) document every meeting but discussed those meetings with senior staff of the FBI and they agreed to not to say anything about it to the investigative team,” Mr Cahill said.

“The fact they went to such lengths to discuss it, document it and then shield the (investigative) team from it, indicates to me that these people believed it was problematic enough to treat it so delicately.”

“All indications are that he was quite concerned about what was going on.”

‘Completely and totally vindicated’: Trump

Mr Trump was quick to hit back with his own spin on Mr Comey’s testimony, releasing a statement through his lawyers that the written account had made him feel ‘completely and totally vindicated’.

“The President is pleased that Mr Comey has finally publicly confirmed his private reports that the President was not under investigation in any Russian probe,” Marc Kasowitz, Mr Trump’s lawyer, said in a statement.

Mr Comey is scheduled to give his testimony in person and be questioned by the Senate committee around midnight Thursday (AEST).