“I don’t care if the mayor is a Democrat or a Republican, they are full of crap when they say the border barrier didn’t help lower the crime rate,” Mr. Trump said, again adding falsely, “It didn’t stay the same. It went way down.”

What Was Said

“If we cut detention space, we are cutting loose dangerous criminals into our country.”

This is disputed.

Before Mr. Trump took the stage, lawmakers in Washington reached a tentative deal on border security that included funding for physical barriers at the border and the reduction of detention space for migrants.

Democrats had sought to limit the number of detention beds under the control of Immigration and Customs Enforcement, arguing that limiting the beds would force the agency to prioritize migrants with serious criminal records. Matt Albence, the deputy director of ICE, said a reduction in the number of beds would mean the release of criminals.

Whether or not ICE would be forced to released hardened criminals is a prediction that cannot be fact checked, but available data suggests that most immigrants in detention have not committed serious crimes. Records obtained by the Transactional Records Access Clearinghouse at Syracuse University show that in June 2018, for example, ICE held more than 44,000 migrants in detention facilities across the country. Of these migrants, 58 percent had no criminal conviction and 21 percent had committed minor offenses such as traffic violations or illegal entry while 18 percent had been convicted of serious crimes.

ICE has disputed that breakdown but used a broader measure for its figures: The agency said 54 percent of detained immigrants had criminal records or faced pending charges, though it did not specify what crimes they were accused of committing.