It takes everything he has in him not to fight right now. A cool calm settles over him, if only because he knows what Cap is trying to do. The only person who could match him for stubbornness is right here in this bed, though, so he's wasting his breath as far as Tony is concerned.
"Who is he, Steve? What do you mean, it's your fault?" Steve would never hand someone over to HYDRA, what gives? His inquiry is gentle, but firm. He's not backing off any time soon.