WASHINGTON — The special counsel, Robert S. Mueller III, removed a top F.B.I. agent this summer from his investigation into Russian election meddling after the Justice Department’s inspector general began examining whether the agent had sent text messages that expressed anti-Trump political views, according to three people briefed on the matter.
The agent, Peter Strzok, is considered one of the most experienced and trusted F.B.I. counterintelligence investigators. He helped lead the investigation into whether Hillary Clinton had mishandled classified information on her private email account, and then played a major role in the investigation into links between President Trump’s campaign and Russia.
But Mr. Strzok was reassigned this summer from Mr. Mueller’s investigation to the F.B.I.’s human resources department, where he has been stationed since. The people briefed on the case said the transfer followed the discovery of text messages in which Mr. Strzok and a colleague reacted to news events, like presidential debates, in ways that could appear critical of Mr. Trump.
“Immediately upon learning of the allegations, the special counsel’s office removed Peter Strzok from the investigation,” said a spokesman for the special counsel’s office, Peter Carr.
The inspector general’s office at the Justice Department said that as part of a larger inquiry it was conducting into how the F.B.I. had handled investigations related to the 2016 election, the office was “reviewing allegations involving communications between certain individuals, and will report its findings regarding those allegations promptly upon completion of the review of them.”
A lawyer for Mr. Strzok did not return several messages seeking comment. A spokeswoman for the Justice Department said that “we are aware of the allegation and are taking any and all appropriate steps.” ABC News reported in August that Mr. Strzok had left the investigation, but the reason for the move was unclear at the time.