Democratic presidential hopefuls on Monday seized Martin Luther King Jr. Day to promote their respective campaign messages even as the 2020 field continues to broaden.

Sen. Kamala Harris Kamala HarrisThe Hill's Campaign Report: Trump and Biden vie for Minnesota | Early voting begins in four states | Blue state GOP governors back Susan Collins Kamala Harris: Black Americans have been 'disproportionately harmed' by Trump Biden town hall draws 3.3 million viewers for CNN MORE (D-Calif.) kicked off the holiday by announcing her candidacy, while Sens. Elizabeth Warren Elizabeth WarrenBiden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon MORE (D-Mass.) and Kirsten Gillibrand Kirsten GillibrandSuburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits The Hill's Campaign Report: 19 years since 9/11 | Dem rival to Marjorie Taylor Greene drops out | Collin Peterson faces fight of his career | Court delivers blow to ex-felon voting rights in Florida MORE (D-N.Y.) and other potential front-runners made public appearances tying their messages to the civil rights leader.

Appearing Monday on ABC's "Good Morning America," Harris declared her bid and said she was honored to do so on Martin Luther King Jr. Day.

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"Today, the day we celebrate Dr. King, is a very special day for all of us as Americans, and I'm honored to be able to make my announcement on the day that we commemorate him," she said.

In announcing her bid, Harris became the latest of several Democratic senators to enter the field.

Another senator who is officially exploring a run, Warren, on Monday equated her message of corporate reform to King's messages during the civil rights era.

"Racial hatred was a critical part of keeping the powerful on top. Dr. King understood what was behind the old 'divide and conquer' strategy, turning working people against other working people," Warren said during Boston's annual MLK Memorial Breakfast, according to WGBH.

"The path to economic security is steep and rocky for millions of working people in America, and it is steeper and rockier for black and brown Americans," Warren added. "When we ignore that fact, then we don't move this nation toward greater equality."

Gillibrand, another Democratic senator who has entered the race, gave her own remarks Monday, speaking in New York at the National Action Network's annual event to commemorate King.

During her speech, Gillibrand called on white women like herself to "amplify your voices" and said she has drawn inspiration from King, according to Politico.

“As a person of deep faith who has been called to public service, I look at Dr. King for inspiration, because his call to action was personal,” she said.

“I am going to run for president of the United States because as a person of faith and as a mother, I cannot sit idly by and not fight for your children as hard as I fight for my own in a time such as this," she added.

Former Housing and Urban Development Secretary Julián Castro (D), another 2020 hopeful, was in San Antonio — where he used to be mayor — to celebrate MLK Day.

Castro, who also announced his White House bid earlier this month, participated in an annual MLK march, where he said called on people to "heed" King's teachings and recognize the "enormous progress" still needed in the U.S.

"It's wonderful to see so many people from different parts of the community to commemorate the legacy of Martin Luther King Jr. and to mark all of the wonderful progress that we've made since his passing, but also to heed his teachings and understand the enormous progress that we still have to make in the country," Castro told Texas Public Radio.

Sanders linked his calls for a "political revolution" to King's calls for racial justice and equality, according to NBC News.