For months now on the campaign trail, Donald Trump has preoccupied himself with mocking Sen. Elizabeth Warren's (D-Mass) identification with Native American lineage. He's derisively called her Pocahontas and, on Monday, insisted that she was a racist for having listed that heritage while on the faculty of Harvard Law School.

The attacks are beyond the norms of traditional campaign behavior. For Trump, however, they're par for the course.

Prior to being the GOP frontrunner, Trump was a real estate tycoon who was trying to hack it as a casino magnate. And while the LA Times reported that he would court Native American tribes when it worked to his advantage, he also routinely targeted their casino operations in hostile, racially provocative terms.

Trump accused the Native-American-run casinos of being fronts for the mob to get unfair tax breaks and avoid anti-corruption regulations. But he didn't stop there. He used racial epithets and funded secretive campaigns to drum up opposition to those casinos. Like with Warren, he questioned whether the main operators were actually Native American at all.

The most famous instance of this came during congressional testimony Trump gave in 1993, when he triumphantly declared: "They don't look like Indians to me and they don't look like Indians to Indians."

Trump would go on to tell radio host Don Imus that same year that he would "perhaps become an Indian myself" if he felt that it might give him an economic advantage. "I think I might have more Indian blood than a lot of the so-called Indians that are trying to open up the reservations," he said. Imus concurred: "A couple of these Indians up in Connecticut look like Michael Jordan, frankly."

Trump took a lot of heat for this. Then-Connecticut Gov. Lowell Weicker called him a "dirtbag" -- to which Trump responded by calling Weicker a "fat slob who couldn't get elected dog catcher in Connecticut." "60 Minutes" ran a segment on the whole affair. And for a while, the real estate magnate begged off talking about the episode saying it would just get him in trouble.

But, over time, Trump became unapologetic about his assessment that Native Americans were not only faking it, but that he could tell as much just by looking at them. In an interview with Steve Forbes in 2011, the topic came up again. And Trump was unbowed.

See the relevant part at 11:39 of this video:

What's happened with the Indian reservations is absolutely unbelievable. The lobbyists have done an unbelievable job. Many of them aren't Indians. I had a very famous statement, 'They don't look like Indians to me.' And they put it on '60 Minutes.' It became a [thing]. And you know what the end of '60 Minutes' was? -- And I didn't relent from that statement. I went before Congress and they said, 'How dare you make that statement?' And I'm sitting here with a room full of people that look just like you Steve and just like me. And they have less Indian blood maybe than we do, okay? And they are running reservations. And I'm saying to myself they don't look like Indians. And I didn't relent. And then at the end of the '60 Minutes' piece the conclusion was, that Trump was right. So, it's a scam and it is huge, it's a huge number of dollars. It's billions and billions of dollars. And the Indian reservation have really hurt other places like Las Vegas and like Atlantic City which pay a lot of tax.

Editor's note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims -- 1.6 billion members of an entire religion -- from entering the U.S.