Natalie Maines is diving headfirst back into political firestorm territory ... more than two decades after the Dixie Chicks controversy that turned country music upside down.

The singer posted a scorching Instagram message Monday aimed at President Donald Trump ... accusing him of destroying democracy and using taxpayer money to help January 6 defendants.

In the post, Maines wrote, "Our democracy is disappearing right before our eyes," before unleashing even harsher language -- calling Trump a "fugly slut" and referencing the Epstein files in a hashtag.

The caption was paired with a carousel that included a close-up image of Donald Trump followed by photos of January 6 rioters storming the U.S. Capitol. She also claimed a previous post using the same insult had already been removed from Instagram ... adding, "We'll see how long this one lasts."

The fiery post immediately brought back memories of 2003 ... when Maines ignited nationwide outrage after criticizing President George W. Bush during a London concert just before the Iraq War.

At the time, the backlash against the Dixie Chicks was brutal -- country stations yanked their songs off the air, fans destroyed CDs and the group became one of the biggest political lightning rods in entertainment. The band later rebranded to The Chicks in 2020.