12:52 PM PT -- Mayor Buttigieg just formally announced that he's running for President of the United States down at an event in his city of South Bend, IN. In his opening speech, he touched on a few simple issues his platform will address, which he says can fit on a bumper sticker.

-- Freedom

-- Security

-- Democracy

Check it out, he gets into the freedom pillar first ... and laid out what he believes the concept means for a modern-day America. Also, he kinda sounds like someone we've heard before on the campaign trail who went on to sit in the Oval. Any guesses?

He went on to say that he recognizes the "audacity" of running for POTUS as a "mid-western millennial mayor" in his mid-30s, but insisted there's no better time for someone like him to make a run at it than right now.

As Mayor Pete puts it, we're living in a time that compels us (and obviously him) to act, adding ... "That's why this time, it's not just about winning an election. It's about winning an era."

Mayor Pete Buttigieg loves to rock ... classic rock, specifically, and he doesn't just listen to it -- turns out the Democratic candidate for President can play some Jimi Hendrix.

The mayor of South Bend, IN, who's expected to officially announce his candidacy Sunday, stopped by our office and downloaded us on his favorite music. Seems he's got a thing for jam bands because he told us the Dave Matthews Band and Phish were his faves during high school and at Harvard.

He also told us his pops got him hooked on Creedence Clearwater Revival, and he's been revisiting those tunes lately. Now, we knew he played guitar growing up ... so we kinda put him on the spot by handing him a Gibson Les Paul.

Mayor Pete didn't disappoint as he started riffin' "Hey Joe" by Hendrix!

During his visit, the candidate, who is openly gay, also talked about the inevitable -- homophobic attacks on the campaign trail ... possibly from President Trump's camp.

Tune in Monday for "TMZ Live" (click here for showtimes) because Mayor Pete chats with us about a whole lot more ... including religion, Kim Kardashian's role in prison reform ... and Lori Loughlin possibly doing hard time for the college admissions scandal.

But, seriously -- politics aside, for just a moment -- it would be pretty cool to have a President who can play Hendrix, right?