Walz actually thought that he was going to make JD Vance drop the facade, and the "Oh fuck" moment is when he realized that unlike Trump, Vance doesn't have a facade.
The guy is 100% legit and that's what the Democrat party and most politicians don't understand about someone like him. You can't make someone look phony if they are being genuine. Everything about JD Vance is genuine, so when they try to go all in on him, he doesn't even need to deflect it like most politicians do. He takes the accusation head on and whether he was wrong or right he speaks his mind and gives a reason.
It's one of the reasons that the loony leftists on places like Reddit and Twitter hate the guy's guts so badly. They want to LARP as Communists and they know that their gender identity is as fraudulent as their politicians.
They are FRAUDS, and the people that they vote for are FRAUDS. Every time JD Vance speaks, and takes accountability or tells the truth, he reminds them that they are frauds. Reckon that must sting like a mother fucker.