Washington (CNN) South Bend, Indiana, Mayor Pete Buttigieg on Wednesday knocked President Donald Trump for abandoning his previous calls for tougher background checks and said the National Rifle Association holds power over the President.

"A 30-minute call with the president of NRA reminded him who's in charge," the South Bend, Indiana mayor said at an event in Iowa.

"Apparently, they have him by the..." Buttigieg began. He then paused for a slight beat.

"Base," he said, eliciting laughter from the crowd.

The 2020 presidential Democratic candidate, who supports universal background checks, said Trump "just can't stand up to" the NRA -- which opposes background check expansion -- and said that puts American lives "at risk."