WASHINGTON (AP) — A former Trump campaign official linked to the Russia investigation by special counsel Robert Mueller has withdrawn his nomination as the Agriculture Department's chief scientist.

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

Questions had been raised about Clovis' qualifications for the administration post. He 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, a former Trump campaign foreign policy adviser 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."

Sen. Debbie Stabenow, a leading Democrat on the Senate Agriculture, Nutrition and Forestry Committee, said Clovis' withdrawal was a "victory for science and our farmers who rely on agricultural research." Stabenow said Clovis' "lack of qualifications and long history of politically divisive statements were disqualifying, and the recent news surrounding his time as co-chair of the Trump campaign has raised even more questions."

The Union of Concerned Scientists, which helped organize a letter signed by more than 3,000 scientists opposing Clovis' nomination, said he had "failed to meet the most basic legal qualifications to serve as the chief scientist at the USDA."

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

A lawyer representing Clovis confirmed this week that Clovis was the person, identified as the "Campaign Supervisor" in court papers, who brought Papadopoulos onto an advisory committee on national security.

In court papers, the unnamed supervisor receives some of Papadopoulos' email exchanges about his attempts to line up a meeting with the Russians, appearing to encourage the effort at one point by responding "Great work." He also later encouraged Papadopoulos to travel to Russia on his own.

The lawyer's statement said Clovis opposed any trip to Russia for Trump or his campaign staff but noted that Clovis may not have made his opposition known when "a volunteer made suggestions on a foreign policy matter."

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

In 2008, Congress spelled out the qualifications of the department's chief scientist, saying that official should come "from among distinguished scientists with specialized training or significant experience in agricultural research, education, and economics."

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