Former Gov. John Hickenlooper (D-CO) speaks at the United States Conference of Mayors winter meeting in Washington, U.S., January 24, 2019.

Montana Governor Steve Bullock talks to the media as he launches a 2020 U.S. presidential campaign in Helena, Montana, U.S., May 14, 2019.

Democratic 2020 U.S. presidential candidate and South Bend Mayor Pete Buttigieg greets voters during a campaign stop at Portsmouth Gas Light in Portsmouth, New Hampshire, U.S., March 8, 2019.

Democratic U.S. presidential candidate U.S. Representative Eric Swalwell (D-CA) visits Torrent Brewing Company in Ames, Iowa, U.S. April 11, 2019.

Potential 2020 U.S. presidential candidate and U.S. Senator Kirsten Gillibrand (D-NY) salutes the crowd of young Democrats during a campaign stop at Stark Brewing in Manchester, New Hampshire, U.S., February 1, 2019.

Former Texas congressman Beto O'Rourke speaks during a campaign stop at The Beancounter Coffeehouse & Drinkery in Burlington, Iowa, U.S. March 14, 2019.

U.S. Rep. John Delaney enters the stage before speaking at the Iowa Democratic Wing Ding in Clear Lake, Iowa, U.S., August 10, 2018. Picture taken August 10, 2018.

U.S. 2020 Democratic presidential candidate and Governor Jay Inslee participates in a moderated discussion at the We the People Summit in Washington, U.S., April 1, 2019.

Democratic 2020 U.S. presidential candidate and U.S. Representative Tulsi Gabbard (D-HI) poses for a photograph with four year-old Akira Hobert (L) and her six year-old brother Jackson during a campaign stop at the Green Elephant in Portsmouth, New Hampshire, U.S., February 17, 2019.

Democratic 2020 U.S. presidential candidate Marianne Williamson talks with child care advocates at the Nevada State Legislature in Carson City, Nevada, U.S., March 14, 2019.

Democratic 2020 U.S. presidential candidate and U.S. Senator Elizabeth Warren (D-MA) speaks to supporters in Memphis, Tennessee, U.S. March 17, 2019.

Democratic presidential candidates and former U.S. Senator Mike Gravel gestures during a candidates' debate at Dartmouth College in Hanover, New Hampshire September 26, 2007.

U.S. Congressman Seth Moulton (D-MA) speaks at a Merrimack County Democrats Summer Social at the Sweet home in Bow, New Hampshire, U.S., July 28, 2018.

Democratic 2020 U.S. presidential candidate and U.S. Senator Bernie Sanders (I-VT) takes the stage at a campaign rally in Concord, New Hampshire, U.S., March 10, 2019.

U.S. 2020 Democratic presidential candidate Julian Castro is introduced to speak to Tri-City Young Democrats in Somersworth, New Hampshire, U.S., January 15, 2019.

U.S. Representative Tim Ryan speaks as he launches his campaign as a Democratic presidential candidate at a rally in Youngstown, Ohio, U.S. April 6, 2019.

U.S. Senator Amy Klobuchar declares her candidacy for the 2020 Democratic presidential nomination in Minneapolis, Minnesota, U.S., February 10, 2019.

WAYNE MESSAM: Messam, 44, defeated a 16-year incumbent in 2015 to become the first black mayor of the Miami suburb of Miramar. He was re-elected in March. The son of Jamaican immigrants, he played on Florida State University's 1993 national championship football team, and then started a construction business with his wife. He has pledged to focus on reducing gun violence, mitigating climate change and reducing student loan debt and the cost of healthcare. Courtesy Wayne for America/Handout via REUTERS

U.S. 2020 Democratic presidential candidate Kamala Harris greets a young supporter at the end of a rally at Texas Southern University in Houston, Texas, U.S., March 23, 2019.

Likely Democratic U.S. presidential candidate U.S. Senator Michael Bennet (D-CO) speaks at the North America's Building Trades Unions (NABTU) 2019 legislative conference in Washington, U.S., April 10, 2019.

Democratic 2020 U.S. presidential candidate and U.S. Senator Cory Booker (D-NJ) takes a photo with supporters after marching across the Edmund Pettus Bridge during the Bloody Sunday commemorative march in Selma, Alabama, U.S. March 3, 2019.

U.S. Democratic presidential candidate Andrew Yang hoists a supporter's sign after speaking at a rally in downtown Los Angeles, California, U.S., April 22, 2019.