The demagogue is one who preaches doctrines he knows to be untrue to men he knows to be idiots.

ALSO

All the odds are on the man who is, intrinsically, the most devious and mediocre — the man who can most adeptly disperse the notion that his mind is a virtual vacuum.
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.

-- H. L. Mencken