Rock legend Bruce Springsteen has denounced US President Donald Trump as a "conman" as he collaborated on a new protest song released Wednesday.

Joe Grushecky, a Pittsburgh-based heartland rocker who has worked in the past with Springsteen but has had much less commercial success, titled his song "That's What Makes Us Great" -- a play on Trump's campaign slogan "Make America Great Again."

An energetic rock tune that sounds like it could have come from Springsteen's E Street Band, the song halfway through features The Boss singing verses on his own.

"Don't you brag to me that you never read a book / I never put my faith in a conman and his crooks," Springsteen sings in clear reference to Trump.

Springsteen and Grushecky come together for a chorus that urges mobilization against Trump.

"It's up to me and you / Love can conquer hate / I know this to be true / That's what makes us great," they sing.

While the song is not his own, it marks some of the most overtly political lyricism of Springsteen's career alongside "American Skin (41 Shots") about New York police officers' 1999 killing of unarmed immigrant Amadou Diallo.

Springsteen -- whose songs have often told the plight of working-class Americans of the type who provided crucial support to Trump -- largely stayed out of direct politics until 2004 when he campaigned for John Kerry in his failed bid to defeat president George W. Bush.

In November, Springsteen joined Hillary Clinton in a major election-eve rally in Philadelphia, where he denounced Trump for his "profound lack of decency," and later played a somber, private show for Barack Obama's staff as they left the White House.

Grushecky told the Pittsburgh Post-Gazette that he wrote the song around the time that Trump took office and that he sent it to Springsteen, who liked it and agreed to give it "the Bruce treatment."

Grushecky said he had been outraged by Trump since the time the tycoon mocked a journalist with disabilities.

"That to me is appalling. I have special needs people in my family and in my neighborhood. I worked with special needs people my whole life, and I was really offended by it," he told the newspaper.