Democratic Sen. John Fetterman Accidentally Calls Himself a Lifelong Republican

Sen. John Fetterman had a major slip of the tongue ... as the centrist Democrat -- who often splits from his party -- called himself a "lifelong Republican."

Fetterman made the gaffe while he was attending the Texas Tribune Festival Saturday ... and the moderator had to remind him that he was in fact a Dem.

Fetterman -- wearing his classic sweatshirt and shorts uniform -- could be seen putting his hand to his head after the viral moment.

He admitted of the mistake ... "I guarantee you that will break through. That will get clipped."

What can we say, John ... when you're right, you're far right. Kidding!

Despite the error ... he firmly responded that he doesn't "have a reason" to join the GOP -- a party he crossed the aisle to side with around 26% of the time in 2025, according to voting stats.

At the same time, Fetterman said ... "If the Democratic Party votes me out or expels me, they’re always entitled to do that."