WASHINGTON (AP) — A former Trump campaign official linked to the Russia investigation by special counsel Robert Mueller has withdrawn his nomination for an agriculture post.

Sam Clovis, a former Trump campaign national co-chairman and chief policy adviser, wrote in a letter to President Donald Trump dated Thursday that he does "not want to be a distraction or a negative influence."

Questions had been raised about his qualifications to serve as the Agriculture Department's chief scientist. Clovis is a self-described skeptic of climate change.

Republicans were preparing to hold a hearing on his nomination next week. But it was revealed this week that Clovis had communications with George Papadopoulos, who has admitted to lying to the FBI about his contacts with Russian intermediaries last year.

In his letter, Clovis said the political climate in Washington "has made it impossible for me to receive balanced and fair consideration for this position."

"The relentless assaults on you and your team seem to be a blood sport that only increases in intensity each day," Clovis wrote. "As I am focused on your success and the success of this Administration, I do not want to be a distraction or negative influence, particularly with so much important work left to do for the American people."

White House press secretary Sarah Huckabee Sanders said: "We respect Mr. Clovis' decision to withdraw his nomination."

Clovis was a professor of economics at Morningside College in Sioux City, Iowa, before he joined the Trump campaign.

If he had been confirmed, Clovis would have overseen the department's nearly $3 billion investment in research and education grants. He also would have helped set the research priorities for the department and ensure that research is conducted with integrity.

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On Twitter follow Ken Thomas at @KThomasDC.