When Donald Trump decided to run for president, he did so by referring to illegal immigrants from Mexico as "murderers" and "rapists." In the months that would follow, Trump often came under-fire for making controversial comments about various other minority groups, leading to a possible conclusion as to why he acts the way he does.

Family affair

Over the last 15 months, critics of the billionaire real estate mogul have accused him of being a racists, a sexist, homophobic, and Islamophobic. While Trump denies all the allegations against him, there might be a scientific explanation for his campaign style and actions.

As reported by PBS on September 29, Trump's documented history can be linked to the theory of eugenics.

In the new PBS documentary titled, "The Choice," biographer Michael D''Antonio explains that Trump was taught at a young age by his father that there are certain people with a superior genetic makeup, which was the reason given to him for why the family had been so successful. Citing the "racehorse theory," D'Antonio elaborates further, noting, "They (Trump family) believe that there are superior people and that if you put together the genes of a superior woman and a superior man, you get a superior offspring."

In a series of clips put together by The Huffington Post earlier this week, it's found that Trump has spoken about superior genes for decades.

"You have to have the right, the right genes," Trump says, while describing himself as a "gene believer," on more than one occasion. The former host of "The Apprentice" is also quoted as saying he was born with a "certain intellect," noting during an interview, "The fact is you have to be born and blessed with something up here (brain)."

Hitler link

Researchers have often linked eugenics and its thought process to the rise of Adolf Hitler during his reign as Chancellor of Germany and head of the Nazi Party for more than a decade in the 1930s and 1940s.

The term "Nazi eugenics" is defined as the Nazi Party's social policies that put the Aryan race above all others, which led the Holocaust and the mass murder of over six million Jews and others in Germany, Poland, and other parts of Europe. In an interesting tie-in to the Hitler theory, Trump is also quoted on the video clip admitting, "You know, I'm proud to have that German blood.

There's no question about it."

Moving forward

At various times throughout the campaign, Trump has had unwanted political allies, including controversial endorsements from members of the Ku Klux Klan and other white supremacists groups, including former KKK Grand Wizard David Duke. Despite the controversy, Trump is only down three points to Hillary Clinton on a national level, though his recent stumble at the first debate is expected to have a negative impact on him in the next round of polling.