(CNN) Rep. Lou Barletta, an immigration hardliner running in a crowded US Senate primary in Pennsylvania, came in contact over the years with fringe organizations and individuals with views far outside the mainstream of American politics, a CNN KFile review of his public appearances over the past decade reveals.

Prior to serving in Congress for the last seven years, Barletta was the mayor of Hazleton, Pennsylvania, where he enacted tough measures to crack down on illegal immigration, including an act that allowed the city to impose fines on landlords who rented to undocumented immigrants and deny permits to businesses who employed them (the ordinance was struck down in federal court).

As mayor, Barletta did an interview with a fringe publication that promotes Holocaust denial and headlined a rally where a political activist and musician who has questioned the Holocaust and promoted conspiracies about the September 11, 2001 attacks also spoke and performed. As a congressman, Barletta appeared on a panel put on by the controversial Youth for Western Civilization and spoke at an event hosted by a journal that pushes extreme anti-immigrant views.

Barletta was an early supporter of Donald Trump's presidential campaign and Trump's immigration agenda. His position has garnered him praise from fellow immigration hardliners in the Republican Party and attracted criticism from immigrant activists and civil liberties groups.

Barletta's positions on immigration and his associations with some of the more extreme elements of the anti-illegal immigration movement will face intense scrutiny in the coming months, particularly if he wins the six-candidate GOP primary to face incumbent Democratic Sen. Bob Casey. A race between the two would in part be a referendum on Trump's immigration policies and rhetoric in a state Trump won by a narrow margin.

In response to questions from CNN's KFile about whether Barletta was aware of the views of the individuals and organizations in this story at the time he associated with them, his deputy campaign manager Jon Anzur said the congressman has always condemned "hate, bigotry, and racial supremacy in all its forms."

"Of course Lou was not aware of these individuals' background. When Lou was mayor, he spoke with people from all over the world who came to Hazleton to report on what was happening," Anzur said in an email statement.

Referring to Barletta's efforts to crackdown on illegal immigration in Hazleton, Anzur added, "This was a global story. As the mayor of a small city, Lou didn't have the resources or staff to screen everyone who asked him questions. On the first day the story broke, Lou did 27 interviews, from World News Tonight to Tucker Carlson. Lou had one assistant, not a team of consultants. He did interviews, not background checks. It would have been impossible to screen every group or reporter who asked him questions."

Azur also pointed to a 2007 episode when a New Jersey Ku Klux Klan organization wanted to demonstrate in Hazleton in support of Barletta's illegal immigration ordinance and Barletta said they weren't welcome in the city, prompting a threat from the group to sue. The spokesman further noted Barletta's renouncement of former Ku Klux Klan leader David Duke in 2008 after Duke endorsed Barletta during his failed congressional bid that year.

A KFile review turned up an October 2006 interview Barletta did with American Free Press, a publication that regularly promotes conspiracy theories including that the Sept. 11, 2001 attacks were a "Jewish plot" and the Holocaust was a hoax . In the interview, Barletta touted his efforts to crackdown on illegal immigration in Hazleton and discussed an ordinance that made English the official language of Hazleton, telling the publication he was just trying to protect the English language.

Barletta's interviewer, American Free Press' "roving editor" Mark Anderson, Anderson is a prominent Bilderberg conspiracy theorist who believes a secretive group of the world's most powerful leaders constitute a de facto one-world government that orchestrates world events. Recently, in 2015, he called into question Jewish author and political activist Elie Wiesel's survival of the Holocaust by putting the term "Holocaust survivor" in quotes while linking to a book arguing that the Holocaust was a hoax.

In June 2007, Barletta headlined a rally at Hazleton City Hall held in support of him and his immigration agenda and in opposition to efforts at the time by the Bush administration to pass comprehensive immigration legislation.

One of the speakers and musical performers at the rally was Paul Topete, lead singer of the "patriot rock" band Poker Face. The band's website, which is now defunct, hosted forums that pushed 9/11 conspiracy theories and Holocaust denial.

When the Anti-Defamation League labeled Topete as anti-Semitic and a Holocaust denier in 2010, the band released a lengthy statement refuting the charges, but said that "asking questions and seeking answers" about the Holocaust "should not be construed as hate, rather it should be a way of mandating historical accuracy." They also said in the statement that it was "not beyond the scope of reasonable doubt" that Israel was involved in 9/11.

In his speech at the rally, available on YouTube , Barletta said the Comprehensive Immigration Reform Act of 2007 would reward millions for breaking the law, including some who are "murders, rapists, thieves, and terrorists" with legal status.

That same year, Barletta appeared in an " exclusive interview" for Americans for Immigration Control, an organization that believes the "annual tidal wave of over a million immigrants (legal and illegal) is endangering our American way of life," according to its website. The interview was part of a short video documentary titled "America — Rule of Law or Anarchy," which according to the group's description of the film, "highlights the fact that people who break our immigration laws are often disposed to break other laws."

The video, which is no longer available for purchase, was written by John Vinson, a founding member of the League of the South, a neo-Confederate group that advocates Southern secession.

Barletta's associations with the more fringe elements of the immigration debate continued when was elected to Congress in 2010.

In 2011, Barletta spoke at an event hosted by The Social Contract, a journal whose editor, Wayne Lutton, argued in a 2010 edition of the journal that "Islam itself is the problem" and called for the end of all Muslim immigration to the US. Lutton spoke repeatedly to the white nationalist Council of Conservative Citizens and was on the board of the white nationalist New Century Foundation. He was also an editorial adviser to the Occidental Quarterly, an online publication that the Anti-Defamation League has labeled "blatantly" anti-Semitic.

In his speech, Barletta spoke about e-Verify legislation and his actions on immigration as mayor of Hazleton.

That same year, at the Conservative Political Action Conference, Barletta appeared on a panel on immigration hosted by the controversial, ultra-conservative student group Youth for Western Civilization, a since-shuttered organization that, according to its website at the time , "focused on the issues of Western history, identity, high culture, and pride as well as opposition to radical multiculturalism, political correctness, racial preferences, mass immigration, and socialism." The group believed that multiculturalism is about "destroying and dispossessing the people and culture of the West, not about an appropriate education about other peoples."

The founder of the group, Kevin DeAnna, appeared on the panel and explained his reasons for opposing illegal immigration.

"I'd go so far as to say that even if you could prove to me, and I couldn't conceive this for a moment, but even if you could prove to me that illegal immigration would help the economy, I would still be opposed to illegal immigration because it's about our dispossession as a people," he said.

For his part, Barletta said, "I'm accused of being a protectionist. Well, you know, at some point there's nothing wrong with protecting America, whether it be our jobs or our people. So I've been called a racist, a bigot, a protectionist, you can call me whatever you want, I call myself an American who's not afraid to stand up for people."

CORRECTION: The headline on this story has been updated to accurately reflect the year in which Barletta did an interview with American Free Press.