The singer, who is of Dominican and Puerto Rican descent, posted a video message to his followers on Instagram Wednesday, explaining why he originally supported 45's reelection bid ... and why he's since retracted his support.

As Jam shared in Spanish ... he originally endorsed Trump's campaign as he thought the businessman would be a "better candidate for the economy," especially for immigrants.

He continued in his statement, which we've translated into English ... "I did not think that a month later, there would be this comedian who would speak badly of my country. For that reason, I renounce my endorsement of Trump."

Jam is, of course, referencing comedian Tony Hinchcliffe's comments from Sunday's rally at Madison Square Garden ... where he called Puerto Rico a "floating island of garbage."

The remark sparked quite a bit of controversy for Hinchcliffe and Trump ... who was criticized for not outright condemning the racist rhetoric when he took the stage at the rally. However, the Trump campaign later announced the joke "does not reflect the views of President Trump."

This isn't the first time Trump has made a misstep when it comes to Jam. As TMZ previously reported, the former prez accidentally misgendered the singer while introducing him as a speaker at his Las Vegas rally in September.

At the time, Trump asked his fans if they knew who Jam was, adding ... "she's hot."

The Republican nominee appeared genuinely surprised when the male Latin artist stepped out to speak ... with Jam choosing to ignore the comment.