Stewart said the GOP presidential candidate's claim over the weekend that Sen. John McCain isn't a war hero raises an important question about Trump.
"What the fuck is wrong with him?" Stewart asked.
When queried about his constant verbal attacks on others on ABC's "This Week," Trump compared it to people who make fun of his hair.
“People are constantly attacking my hair," he told ABC's Martha Raddatz. "I don’t see you coming to my defense. My hair is just fine."
Stewart agreed that attacking someone's physical appearance is a "cheap blow."
"But that hair? That is comedy entrapment," Stewart said. "People are not attacking your hair, they are defending themselves from something that appears like it's about to attack them."
Even GOP rivals who once avoided criticizing Trump are finally speaking out against him -- but Stewart wondered why any of the candidates are surprised by his comments.
“The only reason you liked this guy in the first place is because of the terrible things he was willing to say about Obama," Stewart said. "But Trump has no control over the projectile vomit of dickishness that comes out of his mouth every time he opens it. It was inevitable some of his word puke was gonna get on you.”
Check out the clip above for more, including Stewart's prediction for how Trump could spur a new Jewish holiday.