Actor Kevin Costner speaks ahead of Pete Buttigieg, Democratic presidential candidate and former mayor of South Bend, Indiana, at a campaign event in Exeter, New Hampshire, U.S. February 10, 2020.

Filmmaker Michael Moore speaks during a campaign rally held by Democratic 2020 U.S. presidential candidate and U.S. Senator Bernie Sanders (I-VT) in Sioux City, Iowa, U.S., January 26, 2020.

Actress Cynthia Nixon introduces Democratic U.S. presidential candidate Senator Bernie Sanders during a campaign rally one day before the New Hampshire presidential primary election in Rindge, New Hampshire, U.S., February 10, 2020.

2020 Democratic U.S. presidential candidate and U.S. Senator Bernie Sanders poses for a photograph with a supporter and Hollywood actor and social activist Susan Sarandon during a campaign event at his campaign office in Davenport, Iowa, U.S., August 19, 2019.

Filmmaker Michael Moore speaks during a town hall meeting at La Poste where Democratic 2020 U.S. presidential candidate and U.S. Senator Bernie Sanders (I-VT) is campaigning in Perry, Iowa, U.S., January 26, 2020.

Actor John Cusack introduces Democratic U.S. presidential candidate Senator Bernie Sanders during a campaign town hall event in Exeter, New Hampshire, U.S., January 18, 2020.

Zoe Manville of the band "Portugal. The Man" performs at a Democratic 2020 U.S. presidential candidate and U.S. Senator Bernie Sanders (I-VT) campaign rally in Ames, Iowa, U.S., January 25, 2020.

Singer Lee Greenwood at U.S. President Donald Trump's Keep America Great Rally at the Rupp Arena in Lexington, Kentucky, U.S., November 4, 2019.

The Strokes play a concert at a campaign rally for Democratic U.S. presidential candidate Senator Bernie Sanders at the University of New Hampshire one day before the New Hampshire presidential primary election in Durham, New Hampshire, U.S., February 10, 2020.

Democratic presidential candidate and former South Bend, Indiana mayor Pete Buttigieg, is greeted by actor Michael J. Fox speaks during a campaign event at Keene State College in Keene, New Hampshire, U.S., February 8, 2020.

Actor Tim Robbins introduces Democratic U.S. presidential candidate Senator Bernie Sanders to speak at a campaign stop in Hanover, New Hampshire, U.S., February 9, 2020.

Democratic presidential candidate Pete Buttigieg shakes hands with actor Kevin Costner as he receives his endorsement during a campaign event at a high school in Indianola, Iowa, U.S. December 22, 2019.

The band "Portugal. The Man" performs before Democratic 2020 U.S. presidential candidate and U.S. Senator Bernie Sanders (I-VT) holds a campaign rally in Sioux City, Iowa, U.S., January 26, 2020.