Donald Trump just got challenged about one of his most explosive claims about illegal immigration and he had no proof to back it up

Donald Trump was challenged about one of his most explosive claims regarding immigrants from Mexico during the Fox News' Republican presidential debate on Thursday.

Despite being repeatedly pressed, Trump was seemingly unable to provide real proof for his allegation the Mexican government is deliberately "sending" criminals and other "bad" people to the United States.

Trump first claimed Mexico is "sending people that have lots of problems" to the US at his presidential announcement in June. He said the people being sent across the border by Mexico include "rapists" and people who are "bringing crime" and "bringing drugs." These comments subsequently sparked a massive firestorm. Despite the controversy, Trump doubled down on his claim in an interview with Business Insider and other statements.

During the debate, which featured the ten candidates leading in polls of the GOP primary, moderator Chris Wallace asked Trump to provide evidence backing up his accusation.

"Why not use this first Republican debate to share your proof with the American people?" Wallace asked.

Trump dodged the question and instead claimed his comments have helped bring the issue of illegal immigration into the headlines.

"If it weren't for me, you wouldn't even be talking about illegal immigration Chris. You wouldn't even be talking about it," Trump said. "This was not a subject that was on anybody's mind till I brought it up at my announcement and I said, 'Mexico is sending.' Except the reporters, because they're a very dishonest lot generally speaking in the world of politics, they didn't cover my statement the way I said it. The fact is, since then, many killings, murders, crime, drugs pouring across the border, our money going out and the drugs coming in."

Trump went on to reiterate his desire to build a wall across the border with Mexico. However, he suggested he's open to allowing more people to enter the country from Mexico legally.

Nothing in Trump's response addressed Wallace's question about whether he has any proof to support his allegations about the Mexican government.

"I said we need to build a wall and it has to be built quickly," Trump said. "And I don't mind having a big beautiful door in that wall so that people can come into this country legally, but we need ... to build a wall. We need to keep illegals out."

After Trump's response, Wallace gave him another chance to answer the actual question.

"Mr. Trump, I'll give you thirty seconds," Wallace said. "I'll give you thirty seconds to answer my question, which was, what evidence? Do you have specific evidence that the Mexican government is sending criminals over?"

In his second answer, Trump suggested people have told him Mexico is deliberately sending delinquents into America. However, he still did not provide any specifics.

"I was at the border last week. Border patrol, people that I deal with, that I talk to, they say this is what's happening because our leaders are stupid," Trump said. "Our politicians are stupid and the Mexican government is much smarter, much sharper, much more cunning. And they send the bad ones over because they don't want to pay for them. They don't want to take care of them. Why should they when the stupid leaders of the United States will do it for them? And that's what's happening whether you like it or not."

Trump campaign manager did not immediately respond to an email from Business Insider asking if he has any specific proof of this claim and when he plans to reveal it.

The debate Trump participated in featured the top ten candidates in polls of the Republican primary. Another debate earlier Thursday evening included seven other candidates who are bringing up the rear in the polls.