The Sage of Baltimore may have had it right. H.L. Mencken:
"The larger the mob, the harder the test. In small areas, before small electorates, a first-rate man occasionally fights his way through, carrying even the mob with him by the force of his personality. But when the field is nationwide, and the fight must be waged chiefly at second and third hand, the force of personality cannot so readily make itself felt, then all the odds are on the man who is, intrinsically, the most devious and mediocre — the man who can most adeptly disperse the notions that his mind is a virtual vacuum.

Well, he was right. We're there now.
The Presidency tends, year by year, to go to such men. As democracy is perfected, the office represents, more and more closely, the inner soul of the people. We move toward a lofty ideal. On some great and glorious day the plain folks of the land will reach their heart’s desire at last, and the White House will be adorned by a downright moron."