Whistleblower protection endangered by trump criticism,Lawyer for a whistleblower said whose complaint triggered a US presidential impeachment inquiry.
Since the transcript of his call with the president of Ukraine was revealed, Mr Trump has called for the anonymous whistleblower to be unmasked.
Democrats say the whistleblower will testify to Congress “soon” once steps are taken to protect their identity.
Mr Trump has suggested his opponents could be arrested for treason.
Transcript of a call that President Trump made to Ukraine’s President Volodymyr Zelensky shows he urged him to investigate discredited corruption allegations against former vice-president and 2020 presidential candidate Joe Biden as well as his son.
The call is now at the centre of an effort by Democrats that could see Mr Trump expelled from office, but doing so would require members of his Republican party to turn against him.
The letter from the whistleblower’s legal team – in which the lawyers call attention to Mr Trump’s language was sent to Acting Director of National Intelligence Joseph Maguire on Saturday, and made public on Sunday.
“The events of the past week have heightened our concerns that our client’s identity will be disclosed publicly and that, as a result, our client will be put in harm’s way,” wrote lawyer Andrew Bakaj.
The letter specifically mentions Mr Trump’s call last week for the whistleblower to be identified, as well as the person that supplied the whistleblower with information about the call.
It quotes Mr Trump as saying: “I want to know who’s the person that gave the whistleblower, who’s the person that gave the whistleblower the information, because that’s close to a spy.
“You know what we used to do in the old days when we were smart? Right? With spies and treason, right? We used to handle them a little differently than we do now.”
The letter also references a $50,000 (£40,600) “bounty” that two conservative Trump supporters have offered as a “reward” for information about the whistleblower.
“Unfortunately, we expect this situation to worsen, and to become even more dangerous for our client and any other whistleblowers, as Congress seeks to investigate this matter,” Mr Bakaj’s letter adds.
Mr Maguire faced lawmakers last week and said he believed the whistleblower acted in “good faith”.
Impeachment is the first part the charges of a two-stage political process by which Congress can remove a president from office.
If the House of Representatives votes to pass articles of impeachment, the Senate is forced to hold a trial.
A Senate vote requires a two-thirds majority to convict unlikely is this case, given that Mr Trump’s party controls the chamber
Only two US presidents in history – Bill Clinton and Andrew Johnson have been impeached but neither was convicted and removed.
President Nixon resigned before he could have been impeached.
Whistleblower protection will be endangered if identity will be disclosed publicly.