I'm not so sure about that. I don't think Vance is winning any favor with Trump over the Iran negotiations. That's not even necessarily a critique of Vance, but Trump believes himself to be the world's best negotiator, so if he sends Vance to Iran and Vance comes back with nothing but trash, especially when Vance is the voice of anti-interventionalism in the administration, I think he is going to get cross with Trump. And to be clear, I think literally anybody, no matter how good, who ends up disagreeing with Trump on something will be in his bad graces. But Trump was never an isolationist, so it's just more likely that he and Rubio will be aligned more on foreign policy than he and Vance. Also, as we learned with Obama, the power of the charismatic president does not transfer over well to their endorsements. So Vance may be the heir apparent, but Rubio is still going to be the more marketable politician.