Washington (CNN) The legal team representing the whistleblower who ignited the impeachment investigation has received death threats that have led to at least one law enforcement investigation, according to a source familiar with the situation.

The FBI deemed the threat not to be credible after meeting with the individual who sent it, the source said.

"There have been a myriad of disturbing emails and voicemails sent to the legal team, with a few select messages crossing the line enough into direct threats of harm that have resulted in follow up from relevant law enforcement entities," according to the source.

The Wall Street Journal first reported that the threats had led to at least one law enforcement probe.

Trump has repeatedly derided the anonymous whistleblower whose complaint alleges the President abused his official powers in a July phone call with Ukrainian President Volodymyr Zelensky "to solicit interference" in the 2020 election.

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