"For the president to invoke that word to describe what he's experiencing, as the most powerful man on the face of the planet today, a white man who's enjoyed privilege and power unknown to so many millions more in this country, is one of the most obscene things I've heard him say in an administration that is rife with obscenities," O'Rourke told ABC News' Devin Dwyer, after his weekend stop in Montgomery, Alabama, where he toured the Legacy Museum -- an institution that focuses on the history of slavery and racism in the United States.
The former congressman said Trump poses a "mortal danger" because of the language he uses.
"We saw that brought home to us in El Paso, Texas, on Aug. 3 when a gunman, armed with an AK-47, opened fire in a Walmart, repeating the same words the president had used: warning of an invasion, an infestation of being replaced by Hispanics as a member of the white majority," he said.
O'Rourke reiterated that Trump is a white supremacist, a claim he has made regularly on the campaign trail and in the most recent debate.
"He is, absolutely ... and not only has he brought forward and into the open a racism, an intolerance and a hatred that has long defined the American experience for too many, but he's also directed that and its violence toward populations that don't look like, or love like, or pray like the majority," O'Rourke told ABC News.
Since the mass shooting in his hometown, O'Rourke has made gun reform a centerpiece of his campaign. He's received push back over his mandatory gun buyback program from other moderates in the race, such as South Bend, Indiana, Mayor Pete Buttigieg.
O'Rourke also commented on the Trump administration's recently introduced policy of collecting DNA from migrants crossing the southern border to track them in a national criminal database. The new policy would enable Immigration and Customs Enforcement and the Border Patrol to collect samples from those booked into immigrant detention, Homeland Security officials said Wednesday. The move could target hundreds of thousands of migrants and is likely to prompt a backlash from civil liberty organizations that say genetic data collection should be limited to dangerous criminals.
"This is part of the fear that the president is trying to stoke about immigrants and asylum-seekers and refugees," O'Rourke said. "We know that they arrived at our border as vulnerable, as defenseless, as desperate as a human being can be."
He added, "That's happening in the wealthiest, most powerful country on the face of the planet. … This is absolutely the wrong policy. And to answer your question, no it does not improve the security or safety of our communities or our country."
The DNA collected would be fed into the FBI's Combined DNA Index System, which is used for criminals in police stations across the country, officials said.
The new policy follows the rollout of a rapid DNA testing pilot program earlier this year that Homeland Security said would be used to identify fraudulent claims of family relationships by people crossing the border.
"I want to rewrite immigration laws so that they fully reflect the reality on the ground," O'Rourke said. "I would never criminally prosecute anyone seeking asylum or refuge. I would never incarcerate another family."