Democrats are already testing the waters — or throwing their hats into the ring — for the 2020 presidential election, and a handful of them are participating in highly visible events honoring Martin Luther King Jr. Monday.

Sen. Kamala Harris, the first African-American candidate to officially enter the race, chose MLK Day to announce her intention to do so. Her Monday announcement was intentional, she said.

"The thing about Dr. King that always inspires me is that he was aspirational," the junior senator from California said on ABC's "Good Morning America." "He was aspirational like our country is aspirational. We know that we've not yet reached those ideals. But our strength is that we fight to reach those ideals. So 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 we commemorate him."

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Still other Democrats are honoring the civil rights leader with events in key 2020 locations. MLK Day, in addition to its obvious significance as a day to honor the civil rights leader who helped change the course of American history, is also the first federal holiday after the new year in the unofficial presidential cycle.

New Jersey's Sen. Cory Booker, who has yet to make any announcement on a bid for president, spoke at the National Association for the Advancement of Colored People (NAACP) King Day rally in Columbia, South Carolina. Vermont's Sen. Bernie Sanders, who also hasn't made any official announcements on 2020 at this point, is also in South Carolina for an afternoon town hall at Zion Baptist Church.

Former New York Mayor Michael Bloomberg, another potential 2020 candidate, gave an address at Rev. Al Sharpton's National Action Network Breakfast in Washington. Bloomberg said the late civil rights leader would have made preventing gun violence a top priority if he were still alive today. He also joked that he hasn't spoken with former Vice President Joe Biden Monday, but wants pointers on living in D.C. Biden also spoke at the breakfast.

"He really is my buddy," Biden said of former President Barack Obama, joking, "All those memes are true."

Sen. Kristen Gillibrand, one of three female senators to announce her bid for the presidency so far, attended attending MLK events with Sharpton in Harlem Monday afternoon, along with fellow New York senator, Senate Majority Leader Chuck Schumer. Gillibrand hit Mr. Trump for his demeanor and actions.

"Our president has chosen to tear this country apart … along every line," Gillibrand said. "He's inspired a hate and darkness in this country and he's tearing apart the very fabric of who we are … our very common decency. And that is what we are being called to fight against."

— CBS News' Jack Turman and Richard Escobedo contributed to this report