The singer-songwriter performed during Kamala Harris' Georgia rally Thursday, grabbing his guitar and performing a few acoustic versions of his hit songs before the Democratic nominee for prez hit the stage.

In between songs, Bruce gave his honest opinions on the 45th POTUS ... saying he thinks DJT has more interest in being a dictator than the president -- and saying he's "running to be an American tyrant."

Bruce goes on to say he will only vote for a candidate who believes in the law, peaceful transitions of power and a woman's right to choose -- and, only one candidate meets all that criteria.

Springsteen also says Trump wasn't paying attention in Civics class ... claiming the dude doesn't understand the U.S.A., its history, or what it means to be a true American.

Springsteen wasn't the only celeb stumping for Kamala ... Tyler Perry also came out and fired off a shot about making America a beautiful quilt -- instead of a sheet. Think about it for a second, it'll come to ya.

This all comes on the heels of Kamala's viral Detroit rally ... which saw Harris bring out stars like Eminem to endorse her -- and, feature in a few viral moments along the way.