The singer dropped "Commander in Chief" Tuesday night, and she's already responding to backlash due to the biting lyrics that kick off with ... "Were you ever taught when you were young / If you mess with things selfishly, they’re bound to come undone?"

Unsurprisingly, some fans criticized her for attacking the President and pissing off Republicans who support him ... and even said they were ashamed and could no longer listen to her.

But, Demi doubled down on her stance, and responded to the critics by reminding them she's entitled to political views despite being a celeb ... and she's not just around to entertain her whole life.

She continued by insisting she doesn't give a damn if her new song hurts her, saying ... "I literally don't care if this ruins my career."

Demi adds that her anti-Trump track -- which includes the lyrics, "Commander in Chief, honestly / If I did the things you do, I couldn't sleep" -- stands for something she believes in and it's worth the risk of losing fans.

She concludes by saying as a queer Hispanic woman, she won't be silenced to please an audience.