Hillary Clinton may be no fan of Bernie Sanders, but she says she will support him if Democrats choose him to run against Donald Trump later this year.

"I have my own feelings about him and whether he can win or not," she said on Tuesday (AEST) in a sit-down interview at the Berlin Film Festival. "But if he is the nominee I will support him. Because I think any Democrat is better than Donald Trump. I think Donald Trump is a clear and present danger to our democracy and to the world."

Former US secretary of state Hillary Clinton at a news conference for the film Hillary during the 70th International Film Festival Berlin. Credit:Getty Images Europe

Clinton did 35 hours of sit-down interviews for a four-part documentary Hillary, directed by Nanette Burstein and including frank interviews with Bill Clinton and Barack Obama, that is showing as part of the Berlin Festival's section devoted to long-form television. The only time she shows a flash of fury, as opposed to the measured arguments she uses to dismantle Trump, is talking about Sanders.

"He was in Congress for years. Nobody likes him, nobody wants to work with him, he got nothing done. He was a career politician," she snaps in one episode of the documentary. "Bernie drove me crazy."