President Joe Biden got in a heated exchange with gun control advocate Manuel Oliver on the South Lawn of the White on Monday. Oliver’s 17-year-old son was one of the victims of the 2018 Parkland, Florida high school mass shooting.

After Oliver heckled Biden during the White House’s “celebration of bipartisan gun policy legislation” that Biden signed last month, the president shot back:

“Sit down! You’ll hear what I have to say,” Biden said as Oliver shouted over him.

“You have to do more than this!” Oliver yelled. “You have to open an office in the White House!”

“I’ve been trying to tell you this for years! And years!” Oliver continued while some audience members applauded his remarks.

“We have one. Let me finish my comments,” Biden pushed back, then quickly added, “Let him talk, let him talk.”

“Make no mistake about it, this legislation is real progress, but more has to be done” Biden continued.

The New York Post reports that soon after, Oliver was photographed being escorted out of the South Lawn event.

“There’s nothing to celebrate,” Oliver told the Miami Herald in a phone interview later. “It’s a big lie. We lie between ourselves thinking we have a solution to this when we actually don’t.”

“There was no need for this event,” Oliver added. “At all.”

Later Monday, Igor Volsky, the director of gun control group Guns Down America, tweeted about the event: “POTUS failed to announce next steps today. That’s disappointing.”

The New York Post reports:

The bereaved father had tweeted Monday morning that he was upset about plans to celebrate the new law, which includes enhanced background checks for would-be gun buyers between the ages of 18 and 21.

“The word CELEBRATION has no space in a society that saw 19 kids massacred just a month ago,” Oliver wrote. “‘Most people overestimate what they can do in one year and underestimate what they can do in ten years.’ Not me, not Joaquin.”

In a CNN interview before the event, Oliver said: “It’s like we’re going to a party, to a wedding today … I really wish there were more in this package of bills.”

Oliver has a history of drawing attention to the cause of gun control. In February, on the fourth anniversary of the mass shooting at Marjory Stoneman Douglas High School, he climbed a 150-foot crane near the White House and unfurled a banner that bore a picture of his son’s face and added that “45K people died from gun violence” on Biden’s “watch.”