Nearly 4½ years after he lost his 17-year-old son to a gunman's rampage at a high school in Parkland, Fla., Manuel Oliver did not think it was time to celebrate. 

Oliver was among hundreds who joined President Joe Biden and lawmakers from both parties on the White House's South Lawn on Monday at an event billed as "commemorating the historic achievement of the passage of the Bipartisan Safer Communities Act." Invitees included family members and survivors of mass shootings from Columbine, Colo., to Virginia Tech to Buffalo to Highland Park, Ill.

Oliver, angry that children are still dying - including 19 at an elementary school in Uvalde, Texas, less than two months ago - decided to make his feelings known and stood up while Biden was speaking.

Then he heckled the president.

"Despite the naysayers, we can make meaningful progress on dealing with gun violence," Biden was saying as Oliver, wearing a shirt with his son's photo and message demanding change, cut in to demand the creation of an office in the executive branch focused solely on gun violence.

"Sit down - you will hear what I have to say," Biden said to Oliver, before pausing. "We have one - let me finish my comment." But as Secret Service agents approached Oliver, Biden said, "Let him talk. Let him talk."

Then he continued, "Make no mistake about it - this legislation is real progress. But more has to be done."

The episode highlighted a tension that has run through Biden's presidency and has intensified in recent weeks. Many Democrats have urged the president to do more to take credit for his accomplishments, including a strengthening economy, progress against the pandemic and getting bills through a polarized Congress. At the same time, Biden's advisers are wary of seeming insensitive to voters' concerns and suffering.

In the wake of the Uvalde shooting, Congress passed a bipartisan bill that was the biggest gun control measure in decades - but also fell far short of what advocates wanted. It expanded background checks, funded programs to seize guns from troubled individuals and bolstered mental health services.

Biden touted it Monday, saying, "The provision of this legislation is going to save lives. And it's proof that in today's politics, we can come together on a bipartisan basis to get important things done, even on an issue as tough as guns."

Vice President Kamala Harris echoed the sentiment. "For 30 years, our nation has failed to pass meaningful gun violence legislation," she said, adding, "Because of our president's leadership and because of so many of you, we have passed a law that will make communities around our nation safer."

Oliver said in an interview that he did not appreciate the congratulatory tone "as kids are still dying." He did not regret speaking out, he said after the ceremony. He just wished he had been able to continue talking before being escorted out.

"I've been trying to send a message to President Biden," Oliver said. "Today I had the opportunity to be there. But I'm not going to be part of the celebration."

In February 2018, a gunman opened fire on students and teachers at Marjory Stoneman Douglas High School in Parkland, slaughtering 17 people, including Oliver's son, Joaquin. The mass killing launched a renewed surge of activism as students at the school pushed for tougher gun control measures, though that arguably did not yield significant results until last month.

Other family members had a different reaction at Monday's event. Fred Guttenberg, who lost his daughter, Jamie, in the Parkland shooting, reported on Twitter that he had embraced Sen. John Cornyn, R-Texas, a longtime opponent of firearms restrictions who teamed up with Sen. Chris Murphy, D-Conn., to come up with the compromise that ultimately passed.