Democratic presidential candidate Beto O'Rourke on Sunday invoked the Holocaust while criticizing President Donald Trump's immigration policies during a campaign stop in South Carolina.

During his rally, O'Rourke, a former Texas Democratic Congressman, was discussing how the German transatlantic liner St. Louis with 900 Jewish refugees was turned away by former Democratic President Franklin Delano Roosevelt, resulting in the death of more than 250 of the passengers during the Holocaust.

"In 1939, a ship set sail from the port of Hamburg, Germany with more than 900 Jewish refugees aboard – it’s called the St. Louis. Children, women, and men bound for Cuba," O'Rourke said. "They were going to deboard in the port of Havana, but as they were crossing the Atlantic, Cuba changed their asylum laws and did not allow those passengers to leave. So they set course for the United States. Our president, Franklin Delano Roosevelt, said that that ship could not come to this country, we didn’t have the capacity, this was not our problem."

"The captain of that ship tried to run it aground in Florida, but we sent out Coast Guard cutters to prevent them from doing that, ultimately forcing that ship back across the Atlantic to Europe where more than 250 of her passengers – children, women, and men – were murdered in the Holocaust," O'Rourke continued.

O'Rourke went on to say the "stain is ours to share" even though it was just one man that made the decision, referring to Roosevelt. He then compared the situation to Trump's immigration policy today by saying it is the "decision for family separation and the cruelty with which we treat children in this country today."

"In a democracy, where the people are the government and the government is the people, every single day that these kinds of conditions and situations persist it is on every single one of us," O'Rourke said. "So let’s take this moment to make this commitment – that every single one of us will use our voice and our vote in this democracy to make sure that it is consistent with our interests and our values, and that we’re able to look our kids in the eye in the years to come and tell them at this defining moment of truth we did what was right and we made them proud."

This is not the first time O'Rourke has invoked the Holocaust to attack Trump. Back in April at an Iowa town hall, he likened Trump's rhetoric on immigrants to the "Third Reich," or the Nazi regime, saying, "Now, I might expect someone to describe another human being as an infestation in the Third Reich. I would not expect that in the United States of America," the Times of Israel reported.

In response to the backlash for his rhetoric in April, O'Rourke said he would avoid making these kinds of comparisons because he believed it could affect their chances of defeating Trump.

"If we descend into that pettiness and meanness and those personal attacks, I’m not sure that we can win," O'Rourke said.

Freshman Rep. Alexandria Ocasio-Cortez (D., N.Y.) also received backlash on Tuesday after she compared the crisis at the southern border to the Holocaust during an Instagram live feed on Monday night, the Washington Free Beacon reported.

"They are concentration campus," she said. "I want to talk to the people that are concerned enough with humanity to say that ‘never again' means something, and the fact that concentration are now an institutionalized practice in the home of the free is extraordinarily disturbing."