So I guess my question is, what gives Frank the upper hand over Tusk? I haven't given it a second look yet but it I remember Frank noting that if he's not chosen, the president would only have four days to find a new VP.
Absolutely that. They had already discarded every other candidate. There were only four days left. It was practically impossible to pick, vet and prepare a candidate in such a short time. Much less see if that candidate is amenable to their needs and as capable at passing shit through Congress as Frank. Frank knew that. That was his trump card. And he wasn't at all hostile to working with Trusk. Just not for Trusk. He just wanted to make clear the fact that he wasn't gonna act as their errand boy. Once he got that everything was fine.