Donald Trump can't seem to keep his eyes off Jon Husted's booty ... and Pete Buttigieg thinks the president's fascination with the Ohio senator is truly bizarre.

Charlie and Jacob caught up with the former Transportation Secretary Wednesday in Kalamazoo, Michigan, where he was hosting a get-out-the-vote rally ... and they asked him about Trump's recent praise of Husted's backside, hands, and muscular build.

Buttigieg admits it's a strange thing to notice ... but says Trump's obsession with appearances is just another way to dodge the issues Americans actually care about -- like gas prices and endless war.

When Charlie pressed him on whether Trump thinks Husted's good looks could win over voters, Buttigieg had an interesting theory about how POTUS chooses the people around him.

The conversation then turned to sex appeal in politics ... with Buttigieg joking he might need to hit the gym more himself.

But the real fireworks came when the guys brought up Pete Hegseth's macho image ... prompting Buttigieg to deliver a brutal Pete-on-Pete takedown.

Gotta love election season!!!