President Trump claimed that Joe Biden was “very disrespectful” to his former running mate President Obama. 

“Joe Biden was very disrespectful to President Obama at last night’s debate when he said that he, Joe, ‘was Vice President, not President,’ when trying to make excuses for their failed immigration policies,” Trump wrote on Twitter. “I wonder what ‘O’ was thinking when he heard that one?”

At Thursday’s debate Trump repeatedly hit the Democratic nominee for championing immigration reform during his campaign but failing to bring reform during eight years as vice president. 

“The Obama administration did fail to deliver immigration reform, which had been a key promise during the administration,” NBC’s Kristen Welker, who moderated the debate, asked Biden. “It also presided over record deportations as well as family detentions at the border before changing course. So why should voters trust you with an immigration overhaul now?”

“Because we made a mistake,” Biden said in a shocking admission. “It took too long to get it right. Too long to get it right. I'll be president of the United States, not vice president of the United States.”

BIDEN SAYS HE AND OBAMA 'MADE A MISTAKE' ON IMMIGRATION POLICY 

“And the fact is, and I’ve made it very clear, within 100 days, I'm going to send to the United States Congress a pathway to citizenship for over 11 million undocumented people,” Biden continued. “And all those so called Dreamers, those DACA kids, they're going to be legally certified again.” 

“He had eight years to do what he said he was going to do,” Trump responded. “He did nothing except build cages to keep children in.”

Biden had hit the president for his since-reversed zero-tolerance policy with immigration, which separated “at least 4,000 kids.” Biden noted that since the reversal of the policy, over 500 children remain separated from their parents, who are unable to be located. 

Welker asked Trump if he had a plan to locate the parents of these children. “Yes, we're working on a very -- we're trying very hard. But a lot of these kids come up without the parents, they come over through cartels and the coyotes and through gangs,” he replied. 

Biden refuted Trump’s claim that the 500 children came without parents. 

“Kristen, they did it, we changed the policy. They did it. We changed it. They set up the cages. They -- who built the cages?” Trump said. 

BIDEN SLAMS TRUMP AS HE DISTANCES HIMSELF FROM PROGRESSIVES: 'HE THINKS HE'S RUNNING AGAINST SOMEBODY ELSE'

Trump, bowing to immense political pressure, reversed the child separation policy in June 2018. 

Throughout the debate, Trump repeated the line, “Who built the cages?”

Liberal activists circulated a photo of “cages” housing immigrants at the southern border, but it was later revealed the photo was taken in 2014 during the Obama administration.

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“There was a picture of these horrible cages and they said, ‘Look at these cages, President Trump built them.’ And then it was determined they were built in 2014. That was him,” the president said.