This historian describes President Polk as a "suspicious Machiavellian." As opposed to all those deeply trusting Machiavellians.
Actually, my feeling is that Polk wasn't much of a Machiavellian at all. Suspicious, yes, deeply so, especially when it came to his generals and his political rivals. But not without cause! Taylor and Scott did have political ambitions that were contrary to Polk's and that of his party, and his Secretary of State (Buchanan) frequently acted to advance his own political ambitions at the expense of Polk's foreign policy. Polk did try to marginalize them, by appointing Democratic generals and sending secret envoys on diplomatic missions, but he never tried to get rid of them altogether, which I think a true Machiavellian would have done.