Whosoever wields Mjolnir, if he be worthy, may possess the power of Thor. In Marvel continuity, aside from the lightening God himself, he who is most worthy is Capitan America. Of the best Capitan America comic stories the one where he lifts Thor's hammer is one of the most memorable. It stands to reason then, that in reality, the president of the free world should also be worth enough to possess Mjolnir.
However unlikely it is that even the best presidents could obtain the power of Thor, it is nice to imagine that the American people would hold their commander to the same level of integrity as the Asgardians. Regardless of how reasonable those standards are, there are still some leaders who might compare to Steve Roger's honor or Thor's heart of gold.
That said, Which US presidents are most worthy of wielding Mjolnir?