Updated 12:30 p.m. Nov. 2 - Sam Clovis, who ran President Donald Trump's campaign in Iowa, has withdrawn his nomination to the U.S. Department of Agriculture's chief scientist position. Clovis was linked this week to the federal investigation of Russian interference in the 2016 election.

Clovis sent Trump a letter, dated Nov. 1, that says the political climate "has made it impossible for me to receive balanced and fair consideration for this position" during his Nov. 9 Senate confirmation hearing.

The letter from Clovis also says he is focused on Trump's success, adding, "I do not want to be a distraction or negative influence, particularly with so much important work left to do for the American people."

Clovis faced opposition from thousands of scientists, who believed he was not the right man for the position of the USDA's undersecretary for research, education and economics. The former conservative talk show host from Iowa is a self-described climate change skeptic.

When asked for comment, the USDA says in an email that it is "Dr. Clovis' decision."

Original story from Oct. 31 - As U.S. Department of Agriculture chief scientist nominee Sam Clovis prepares for next week's Senate confirmation hearing, he's been linked to the federal investigation of Russian interference in the 2016 election and is the target of another round of opposition from thousands of scientists.

Clovis is the Trump "campaign supervisor" mentioned in court documents released Monday by the special counsel, according to the Washington Post. The former conservative radio host encouraged Trump advisor George Papadopoulos in an email to meet with Russian officials.

Senate Agriculture Chairman Pat Roberts, R-Kansas, told Politico that Clovis, who ran Trump's Iowa campaign, has been "a fully cooperative witness" in the separate Senate Intelligence Committee investigation into the election.

The revelation comes as Clovis is waiting to be confirmed as the USDA's undersecretary for research, education and economics; a hearing is slated for Nov. 9. Iowa Republican Sen. Chuck Grassley was asked Tuesday whether Clovis should withdraw his nomination. He says it's too early to make that call.

"One thing that would make a big difference to me is the extent to which Sam Clovis is committed to cooperating with the special counsel," Grassley says. "It would be stupid for him not to."

Court documents describe several emails between Papadopoulos and top campaign officials for now-President Donald Trump. Papadopoulos has pleaded guilty to lying to federal agents about his contact with a professor who has ties to the Russian government.

The Trump campaign asked Clovis to put together a national security advisory committee, according to an emailed statement from law firm diGenova & Toensing, which is representing Clovis.

"Among the members was George Papadopoulos, who attended one meeting and was never otherwise approached by the campaign for consultation," the statement reads. It also says Clovis "vigorously opposed" trips to Russia within the campaign.

"If a volunteer made suggestions on any foreign policy matter, Dr. Clovis, a polite gentleman from Iowa, would have expressed courtesy and appreciation," the statement reads.

Beyond the Russia probe, Clovis' qualifications for chief scientist position again are being called into question. More than 3,000 scientists signed a letter that was sent this week to Senate Agriculture Committee members Roberts and Michigan Democratic U.S. Sen. Debbie Stabenow, urging the panel to reject Clovis' nomination.

"His professional background is completely devoid of relevant scientific experience that would otherwise equip him to fulfill his duties," the letter reads. "An individual without grounding in the scientific process is ill-suited to make informed, objective, and strategic investments for the future of American agriculture."

The U.S. code establishing the undersecretary position says he or she should be selected from "among distinguished scientists with specialized training or significant experience in agricultural research, education, and economics."

Katarina Sostaric is a reporter for Iowa Public Radio in Iowa City, Iowa. Follow her on Twitter: @KatarinaSos