Democratic presidential hopeful Julián Castro heard about President Trump’s rally in Panama City Beach, Florida, on Wednesday night—and he’s not having it.

“The president,” he said in an interview with Mother Jones on Thursday, “is being a grade-A idiot.”

Trump was speaking about the tens of thousands of migrants at the US-Mexico border when he started talking about Border Patrol agents using deadly force. “And don’t forget—we don’t let them and we can’t let them use weapons,” Trump said. “We can’t. Other countries do. We can’t. I would never do that. But how do you stop these people? You can’t. There’s—”

From the crowd, a woman reportedly yelled out, “Shoot them!”

The president paused before deadpanning, “That’s only in the Panhandle you can get away with that stuff. Only in the Panhandle!”

Trump muses about shooting undocumented immigrants but says he wouldn't do it pic.twitter.com/2UWXIvvRad — Aaron Rupar (@atrupar) May 9, 2019

In an exclusive interview in San Antonio, Castro slammed Trump, calling his behavior “unbecoming of a president.”

“I mean, the president is being a grade-A idiot,” he said. “Entertaining the idea that you would shoot a human being just because they’re looking for a better life. You know, somebody can think that that’s all fun and games, but we’ve already seen during this administration the level of hate crimes increase. We’ve seen so many white supremacists go out there and say that they’re inspired by President Trump and shoot people. And so he’s being a grade-A idiot.

“To continue to foster the flames of division like that, that is unbecoming of a president, of anybody in public office.”

For the full interview with Julián Castro, listen to next week’s episode of the Mother Jones Podcast.