Against Sanders maybe
If the argument is Paul would do well against Hillary because he'd beat her on foreign policy and civil liberties (not that I buy it), that edge would be negated against Sanders, whose economic views are much more popular than Paul's. I bet Sanders could get 55 against Paul, assuming the absence of an independent run. There of course would be an independent run but if we're saying Paul and Sanders will be the nominees, I assume the rule is pretend whatever the hell you want.
Apologies in advance for inspiring someone to start a Paul vs Sanders vs Bolton thread. I'll be annoyed about it too.