WASHINGTON — A former Trump campaign aide dropped out of the running on Thursday for a senior position at the Department of Agriculture three days after his name was tied to a former campaign foreign policy adviser who pleaded guilty to lying to the F.B.I. over his contacts with Russia.

The campaign aide, Sam Clovis, told President Trump that he decided to withdraw from consideration to be the chief scientist at the Department of Agriculture, the White House said.

“The political climate inside Washington has made it impossible for me to receive balanced and fair consideration for this position,” Mr. Clovis wrote in a letter on Wednesday to Mr. Trump. Mr. Clovis’s qualifications to be the chief scientist at the department have been questioned, as he is not a scientist himself. “The relentless assaults on you and your team seem to be a blood sport that only increases in intensity each day.”

Mr. Clovis’s request to drop out of consideration is the latest blow to the Trump administration that for months has been dogged by the special counsel investigation into possible ties between the Trump campaign and Russia. Mr. Clovis, an early campaign adviser, has met with the special counsel’s team.