WATCH: Trailer for Barney Frank Doc Premiering at Tribeca Film Fest

He's been called the most irascible and the most intelligent member of Congress. Now that he's retired, Barney Frank, the former U.S. Representative from Massachusetts will have to contend with being the smartest and most incorrigible member of Congress, past or present.

In Compared to What: The Improbable Journey of Barney Frank, filmmakers Sheila Canavan and Michael Chandler (aided by executive producer Alec Baldwin) had rare access to the personal life of America's most prominent gay politician, whose career spanned 40 years.

A trailer for the film, which premieres on Sunday, April 27, at the Tribeca Film Festival, gives a peek into the life and work of a man obsessed with public service.

The documentary encompassed the time from Frank's coming out in 1987 (he was the first congressman to do so voluntarily) until his wedding to Jim Ready in 2012.

"I regretted not coming out earlier," Frank says. "My life was considerably improved when I wasn't hiding things. Plus, I think it had a good political effect on prejudice."

As for an openly gay president? It'll be a little while, at least, says Frank: "That's at least 20 years or more off. James Buchanan was gay, but he was also the worst fucking president, so there's no point in claiming him."

Watch the trailer.