Democratic U.S. presidential candidate Tom Steyer goes to shake hands at the end of a campaign event in Yemassee, South Carolina, U.S., February 23, 2020.

Democratic U.S. presidential candidate Senator Bernie Sanders takes the stage for an outdoor campaign rally in Austin, Texas, U.S., February 23, 2020.

Supporters of U.S. Democratic presidential candidate Senator Elizabeth Warren cheer during a campaign rally in Denver, Colorado, U.S., February 23, 2020.

A figurine of U.S. Democratic presidential candidate Senator Elizabeth Warren sits on the podium during a campaign rally in Denver, Colorado, U.S., February 23, 2020.

People hold signs as they gather for the town hall held by Democratic presidential candidate and former mayor of South Bend, Indiana, Pete Buttigieg at Washington-Liberty High School in Arlington, Virginia, U.S., February 23, 2020.

Democratic 2020 U.S. presidential candidate former South Bend, Indiana Mayor Pete Buttigieg attends a campaign event in Denver, Colorado, U.S., February 22, 2020.

U.S. Democratic 2020 presidential candidate Senator Elizabeth Warren poses for photos at a campaign rally at the Seattle Center Armory in Seattle, Washington, U.S. February 22, 2020.

A woman watches through a window as Democratic 2020 U.S. presidential candidate and former South Bend, Indiana Mayor Pete Buttigieg (not pictured) speaks during a church service at First Baptist Church of James Island in Charleston, South Carolina, U.S., February 23, 2020.

Democratic presidential candidate and former mayor of South Bend, Indiana, Pete Buttigieg greets attendees following a town hall at Washington-Liberty High School in Arlington, Virginia, U.S., February 23, 2020.

A woman wears a button in support of Democratic U.S. presidential candidate Tom Steyer during a campaign event in Hampton, South Carolina, U.S., February 23, 2020.

U.S. 2020 Democratic presidential candidate Senator Bernie Sanders speaks at a campaign rally in Houston, Texas, U.S., February 23, 2020.

A woman grabs a button before U.S. 2020 Democratic presidential candidate Senator Bernie Sanders speaks at a campaign rally in Houston, Texas, U.S. February 23, 2020.

Democratic U.S. presidential candidate Senator Bernie Sanders speaks an outdoor campaign rally in Austin, Texas, U.S., February 23, 2020.

U.S. Democratic presidential candidate Senator Elizabeth Warren speaks to supporters during a campaign rally in Denver, Colorado, U.S., February 23, 2020.

Democratic U.S. presidential candidate and former U.S. Vice President Joe Biden meets with people outside a Community Resource Center in North Charleston, South Carolina, U.S., February 24, 2020.

Democratic U.S. presidential candidate Senator Bernie Sanders speaks during a campaign rally at the University of Houston in Houston, Texas, U.S., February 23, 2020.

Supporters of Democratic U.S. presidential candidate Senator Bernie Sanders cheer as he takes the stage for an outdoor campaign rally in Austin, Texas, U.S., February 23, 2020.

Democratic U.S. presidential candidate and former U.S. Vice President Joe Biden talks through the open window of his vehicle as he leaves a Community Resource Center in North Charleston, South Carolina, U.S., February 24, 2020.

Democratic U.S. presidential candidate Tom Steyer laughs at the end of a campaign event in Yemassee, South Carolina, U.S., February 23, 2020.

Democratic U.S. presidential candidate and former U.S. Vice President Joe Biden speaks at Sunday services at Royal Missionary Baptist Church in North Charleston, South Carolina, U.S., February 23, 2020.

Democratic U.S. presidential candidate and former South Bend Mayor Pete Buttigieg marches with striking McDonald's workers while campaigning in Charleston, South Carolina, U.S., February 24, 2020.