Sam Clovis was an early supporter of President Trump during the 2016 campaign. (Charlie Neibergall/AP)

Former Trump campaign co-chairman Sam Clovis is facing renewed opposition to his nomination to serve as the Agriculture Department's chief scientist amid revelations that he encouraged a campaign adviser to foster ties with Russian officials.

On Tuesday, several thousand scientists and researchers affiliated with two national organizations that have rallied against Clovis's nomination signed letters urging the Senate Committee on Agriculture, Nutrition and Forestry not to confirm him, calling him unfit for the post.

The former conservative radio talk-show host from Iowa was already a controversial choice to be the department's chief scientist. Clovis, who is not a trained scientist, is a climate change skeptic who has said protecting gay rights could lead to the legalization of pedophilia.

"In every aspect, Clovis falls far short of the standards demanded by the position," the Union of Concerned Scientists wrote in a one-page letter to the committee's chairman, Sen. Pat Roberts (R-Kan.), and the panel's top Democrat, Sen. Debbie Stabenow (Mich.). The letter had 3,100 signers.

[Trump just nominated a climate change skeptic to USDA’s top science post]

Mike Lavender, senior Washington representative for the Food and Environment Program at the Union of Concerned Scientists, said in a statement that "emerging evidence of Clovis' potential involvement with the Trump campaign's Russian connections should be the final nail in the coffin for his confirmation."

The Center for Science in the Public Interest sent the committee a similar letter Tuesday.

A lawyer for Clovis, who is currently a senior White House adviser to the Agriculture Department, did not respond to a request for comment.

The new round of opposition came after Clovis was identified as one of the top officials on the Trump campaign who was aware of efforts by foreign policy adviser George Papadopoulos to broker a relationship with Russian officials.

Court documents unsealed Monday revealed that Papadopoulos pleaded guilty in early October to making false statement to FBI investigators about his contacts with foreigners claiming to have high-level Russian connections.

In August 2016, Clovis encouraged Papadopoulos to organize an "off the record" meeting with Russian officials, according to court documents. "I would encourage you" and another foreign policy adviser to the campaign to "make the trip, if it is feasible," Clovis wrote. The meeting did not ultimately take place.

Clovis's attorney, Victoria Toensing, told The Washington Post on Monday that her client "always vigorously opposed any Russian trip for Donald Trump and/or the campaign." She said his responses to Papadopoulos were a courtesy by "a polite gentleman from Iowa."

[Top campaign officials knew of Trump adviser’s outreach to Russia]

Clovis is likely to face questions about his interactions with Papadopoulos during his Senate hearing, which had been tentatively scheduled for Nov. 9.

"The emerging information about his role in the Trump campaign's interactions with Russia raises serious concerns," Stabenow said in a statement. "As we consider his nomination, I will be looking into these facts, along with his questionable qualifications and long history of divisive and outrageous statements."

Roberts spokeswoman Meghan Cline declined to comment on the opposition to Clovis, saying that "we are working on scheduling details and will announce a date for a nominations hearing soon."

A former economics professor at Morningside College in Iowa, Clovis made an unsuccessful run for the U.S. Senate in 2014. He served as one of Trump's first campaign policy advisers. In a 2014 interview with Iowa Public Radio, he said he was "extremely skeptical" about climate change.

Clovis took a leave of absence from his position at Morningside College in 2015 to join the Trump campaign as a chief policy adviser. He helped develop Trump's campaign proposal to ban Muslims from entering the United States, drawing opposition from some university administrators, a university spokesman told the outlet Iowa Starting Line.

Trump nominated him in July to be the Agriculture Department's undersecretary of research, education and economics, a top science position that oversees the agency's extensive scientific mission. The chief scientist also oversees the economic bureaus, including the Natural Agricultural Statistics Service and the Economic Research Service.

Clovis has a BS in political science, an MBA and a PhD in public administration, according to the White House. But the undersecretary for research job has traditionally been held by people with advanced degrees in science or medicine.

The 2008 farm bill specifies that appointees to the post should be chosen "from among distinguished scientists with specialized training or significant experience in agricultural research, education, and economics." The measure noted that the job is "responsible for the coordination of the research, education, and extension activities of the Department."

Tom Hamburger contributed to this report.