sanders

Democratic presidential candidate Bernie Sanders speaks during a campaign event on Monday in Richmond, Calif. The independent senator identifies as a democratic socialist. Justin Sullivan/Getty Images hide caption

Democratic presidential candidates, Sen. Bernie Sanders (left), Sen. Amy Klobuchar and businessman Tom Steyer raise their hands during a Democratic presidential primary debate on Friday at Saint Anselm College in Manchester, N.H. Elise Amendola/AP hide caption

Former Vice President Joe Biden speaks as Sen. Bernie Sanders listens during the Democratic Presidential Debate on Nov. 20, 2019 in Atlanta. Alex Wong/Getty Images hide caption

Left to right: former Vice President Joe Biden, Massuchusetts Sen. Elizabeth Warren and South Bend, Ind., Mayor Pete Buttigieg react on stage during the Democratic presidential debate at Otterbein University. Win McNamee/Getty Images hide caption

Ten democratic presidential candidates appear onstage before the start of the Democratic Presidential Debate at Texas Southern University in Houston on Thursday. Win McNamee/Getty Images hide caption

Sen. Bernie Sanders speaks during a campaign rally in June 2016 at Qualcomm Stadium in San Diego, Calif. He launched a second presidential campaign on Tuesday, with a big burst of donations from supporters, but new challenges ahead. Sandy Huffaker/AP hide caption

Sen. Bernie Sanders of Vermont speaks to the press in November. Sanders hasn't officially decided on another presidential run — yet. Zach Gibson/Getty Images hide caption

Sen. Cory Booker of New Jersey addresses a crowd in New Hampshire, which happens to be a key early presidential primary state. Michael Swensen for The Boston Globe via Getty Images hide caption

DNC Chairman Tom Perez has called for the party to reform the way it uses superdelegates in its presidential nominating process. George Frey/Getty Images hide caption

President Obama and Hillary Clinton stand together on stage on the third day of the Democratic National Convention in Philadelphia. Justin Sullivan/Getty Images hide caption

Former President Bill Clinton walks off stage after delivering remarks at the Democratic National Convention in Philadelphia on Tuesday. Aaron P. Bernstein/Getty Images hide caption

Workers prepare the podium Sunday ahead of the Democratic National Convention at the Wells Fargo Center in Philadelphia. Drew Angerer/Getty Images hide caption

Brooke Peterson poses for photos with a sign at a rally for Democratic presidential candidate Sen. Bernie Sanders, I-Vt., on Tuesday in Carson, Calif. Jae C. Hong/AP hide caption

Democratic presidential candidate Bernie Sanders says his campaign and supporters were not treated fairly during last Saturday's Nevada Democratic convention. Charlie Neibergall/AP hide caption

Republican Ted Cruz makes a campaign stop at the Bravo Cafe Monday in Osceola, Ind. The Hoosier State might be Cruz's last chance to stop Donald Trump from getting the nomination. Joe Raedle/Getty Images hide caption

Hillary Clinton waves to a crowd at a Women for Hillary event at the New York Hilton hotel Monday in Midtown Manhattan. Kathy Willens/AP hide caption

Bernie Sanders and Ted Cruz celebrate with supporters after winning the Wisconsin primary contests on Tuesday. Brennan Linsley and Paul Sancya/AP hide caption

Republican Ted Cruz (left) addresses the media after a campaign rally earlier this month in Kansas City, Mo.; Democrat Bernie Sanders speaks at a town hall event last week in Milwaukee. Polls ahead of Tuesday's Wisconsin primary contests gave Cruz and Sanders narrow leads. Kyle Rivas (L) and Darren Hauck (R)/Getty Images hide caption

Confetti falls on the head of John Kasich, governor of Ohio and a 2016 Republican presidential candidate, after speaking during a campaign event in Berea, Ohio, on Tuesday. Kasich secured his first victory on Mega Tuesday. Ty Wright/Bloomberg via Getty Images hide caption

Audience members hold up signs supporting Republican presidential candidate Donald Trump during a campaign rally in Boca Raton, Fla., on Sunday. Paul Sancya/AP hide caption