California Rep. Eric Swalwell, one of President Trump's most outspoken critics in Congress, announced he is seeking the presidential nomination in what is shaping up to be the largest Democratic primary field in U.S. history.

The 38-year-old San Francisco area lawmaker announced his presidential campaign during an appearance on "The Late Night Show with Stephen Colbert" that aired Monday night on CBS.

"I've already done a lot, but I can do more," he said in a clip released by the show. "I've been in Congress for six years. I've defended our country from the Intelligence Committee while Democracy has been on the ropes."

Rep. Eric Swalwell appears on "The Late Show with Stephen Colbert" on Mon., April 8, 2019. Scott Kowalchyk/CBS Broadcasting Inc.

Swalwell enters a crowded race for president with more than a dozen candidates seeking to capture the Democratic nomination and thwart Mr. Trump's reelection bid next year. To date, 17 other Democrats have declared their candidacy for president or launched presidential exploratory committees, including Sens. Bernie Sanders, Kirsten Gillibrand, Kamala Harris, Cory Booker and Elizabeth Warren; Ohio Rep. Tim Ryan; Hawaii Rep. Tulsi Gabbard; Texas Rep. Beto O'Rourke; and South Bend, Indiana, Mayor Pete Buttigieg.

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Under the Trump administration, Swalwell, a four-term lawmaker and member of the House Intelligence and Judiciary Committees, has solidified himself as one of the leading detractors of the White House, constantly appearing on cable news to condemn the president's policies and defend special counsel Robert Mueller's now-completed investigation.

With the release of the Justice Department summary of Mueller's report — which said the special counsel found no evidence of collusion or coordination between the Trump campaign and the Russian government — Swalwell will make gun safety reform his top agenda item on the campaign trail.

"I've talked to kids who sit in their classroom afraid that they'll be the next victim of gun violence. I see Washington do nothing about it after the moments of silence. And I see lawmakers who love their guns more than they love our kids," Swalwell said Monday. "And none of that is gonna change until we get a leader who's willing to go big on the issues we take, be bold in the solutions we offer and do good in the way that we govern."

"I'm ready to solve these problems," he added.

Last week, the California Democrat shared a voicemail his office received in which an individual is heard making a death threat against him because of his stance on gun rights. "We're going to war. And you're going to be the first motherf***ing casualty," the person in the voicemail posted by Swalwell on Twitter is heard saying.

In his post, Swalwell wrote, "I'm not afraid of this guy. I'm not afraid of the NRA. I'm not afraid. No fear. #EndGunViolence."

I'm not afraid of this guy. I'm not afraid of the NRA. I'm not afraid. No fear. #EndGunViolence pic.twitter.com/KcB1FRKnKR — Rep. Eric Swalwell (@RepSwalwell) April 3, 2019

Swalwell, who has been participating in events in Iowa, his home state, in recent months, is also hosting a town hall on gun control in Florida on Tuesday alongside survivors of the Stoneman Douglas High School massacre, in which 17 students and staff members were killed by a gunman.

Before his congressional tenure, Swalwell earned his J.D. from the University of Maryland and was a congressional intern for former California Rep. Ellen Tauscher.