I admit I am a bit naive when it comes to politics, but I'm talking about if he becomes president. Wouldn't he be leading the party if that happened?
Leading the party doesn't means that he can take important decisions without consulting anyone. Take Obama for example. He was against sending weapons to the Kiev junta. But the Americans ultimately decided to send weapons to the junta, as Biden and Billary was in favor of it. That said, there are places where leading the party means that you can take all the decisions without consulting anyone. North Korea for example.