(CNN) Sam Clovis, Donald Trump's pick to be chief scientist for the Department of Agriculture, pushed unfounded theories about then-President Barack Obama's upbringing and called then-Attorney General Eric Holder a "racist black," a CNN KFile review of Clovis's writings and radio broadcasts during 2012 and 2013 has found.

Clovis was a conservative radio host and political activist in Iowa before gaining national attention as one of the more vocal supporters of Trump during the presidential campaign. His nomination to head science at the USDA requires Senate confirmation.

CNN's KFile reported last week on blog posts from 2011 and 2012 in which Clovis called black leaders "race traders" and accused Obama of being a "Maoist." CNN's KFile has since obtained the transcripts of some episodes of Clovis' radio show, "Impact with Sam Clovis," reviewed hours of available audio of Clovis' radio appearances, and uncovered previously unreported blog posts by Clovis. (Read CNN KFile's full research here .)

The material shows how Clovis regularly engaged with fringe theories that were prevalent in the right-wing radio and blogosphere during Obama's presidency.

Clovis did not return a request for comment. The White House also did not respond to emails requesting comment.

On Friday, a USDA spokesperson told CNN's KFile that Secretary of Agriculture Sonny Perdue still supports Clovis to be the under secretary for research, education, and economics.

"Nothing has changed. The Secretary supports Dr. Clovis to be the undersecretary for REE completely," the spokesperson said. The spokesperson declined to comment on any of Clovis' specific comments included in the CNN KFile report.

In a 2012 blog post archived on the website for the Sioux City-based radio station KSCJ, Clovis raised questions about Obama's biography that echoed some of the theories pushed by those in the birther movement who claim that Obama isn't an American citizen.

"For over a decade, Obama allowed his publisher to carry a biography that had him born in Kenya. Only after beginning his pursuit of public office did he 'correct' the entry," Clovis wrote. (The literary agent who edited the biography has said the error was hers, and that she made it with no direct communication with Obama.)

Clovis then theorized that Obama's past connections to left-wing figures went unscrutinized by the media because Obama is black.

"Could it be that the first African-American president is being given a pass because he is Black? How incredibly racist is that? The logical conclusion is that because he is Black, he cannot help himself. This kind of thinking is the absolute worst," Clovis wrote.

Clovis also discussed the race of Holder and then-Secretary of Labor Tom Perez, who now heads the Democratic National Committee. In a 2013 episode of "Impact with Sam Clovis," Clovis called Holder "a racist black" and Perez "a racist Latino."

"This goes right in line with Tom Perez who is a racist Latino and goes to (inaudible) who is a racist Latino, Eric Holder who is a racist black," according to a transcript of the show obtained by CNN's KFile.

Clovis similarly labeled Holder "a racist bigot" in a blog post from April 2012. Clovis doesn't make clear in either instance why he believes Holder and Perez are racist.

Clovis would frequently attack prominent Democratic leaders with insults and epithets. He called then-Senate Majority Leader Harry Reid "mentally ill" during a September 2013 local Iowa radio appearance and referred to House Minority Leader Nancy Pelosi as "the Batwoman of Alcatraz" and said "something's happened to her brain" in a May 2013 episode of "Impact with Sam Clovis.

Clovis also denied the veracity of climate change science, a belief cited by Senate Democrats and climate activists who have expressed opposition to his nomination for the USDA job.

Clovis told Iowa radio host Jan Mickelson in June 2013 that climate change wasn't settled science and argued that progressives changed the term from "global warming" to "climate change" to imply they were going to create the ideal climate around the world.

"What we have to examine is how the language changes, and when you start to go away from 'global warming' to 'climate change,' this goes right into the heart of progressive thinking because what it says, or what the implication is, is that somehow the progressives are going to figure out a way to create the ideal climate in all regions of the earth," he said. "And so how nonsensical is that? If you follow that logic to its logical conclusion, that's the conclusion in which you arrive -- is that there is some perfect weather or some perfect climate that we will have for everyone -- everyone will thrive."

Speaking with the same Iowa radio host in February 2014, Clovis agreed with Mickelson's assessment that climate change was a way to redistribute wealth and "a big hustle." Clovis also made reference to "Agenda 21," a United Nations action plan on sustainability that right-wing figures have long claimed is an attempt by the internal organization to strip local governments of their sovereignty.

Clovis repeatedly engaged in conspiratorial theories, particularly ones that cast the Obama administration in the most sinister light.

In a April 2012 blog post , Clovis expressed his belief that Obama wanted to rule as a dictator and enslave his opponents.

"This president is a dangerous person," Clovis wrote. "He is dangerous in that he does not have the interests of the nation in mind and is more than willing to do anything to advance an ideology that is absolutely opposed to American exceptionalism. Four more years of this man as president could very well mean the total deconstruction of our Constitutional republic. He wants to be a dictator and he wants to enslave all who are not part of his regime. As Althusius advised in the 17th Century, we have a right to throw off imprudent magistrates. The current president certainly qualifies. Vote in November."

In a September 2012 episode of his online radio program "Serious Civics with Sam Clovis," Clovis observed that Obama appeared "happy" after the attack on the American embassy in Benghazi, Libya that month.

"This is something that tells you that he is dismissive of the entire affair and in fact, I would even hate to stretch this out but it's almost as if it was intentional. As if he is happy that these things have occurred." Clovis said. "Now I know that's harsh and I don't have any evidence to support that. But look at his actions. Right after the event, where does he go? He goes and he does an interview on the hip hop guy who is a pimp and on top of everything else. The fact that he goes to Las Vegas and essentially just mentions in passing that we've had four Americans killed in Libya under a premeditated orchestrated attack and he doesn't seem to have any more attachment to it than that. This is frightening."