Sen. Bernie Sanders (I-Vt.) and Robert F. Kennedy Jr. got into it over baby onesies during Wednesday’s confirmation hearings, and “Late Show” host Stephen Colbert couldn’t help but laugh.

“That’s such an intense grilling with such silly words,” Colbert said.

Kennedy, who was nominated by President Donald Trump to lead Health and Human Services, claimed during the hearings that he favors vaccines.

But lawmakers weren’t buying it given his history of anti-vaccine activism.

Sanders in particular pointed out that a group Kennedy founded is selling onesies ― a one-piece outfit for infants ― with anti-vaccine slogans on it, which led to a memorable debate... which Colbert enhanced by breaking out his Sanders impression.

Check it out in the Wednesday night monologue: