The United States has had some extraordinary presidents. Lincoln was a master wordsmith; Jefferson a true renaissance man; Hoover a brilliant manager. When comparing presidential intelligence, though, I see plenty of room for error. What made a man intelligent in the 18th century could differ from what makes a man intelligent in the day. Managerial and administrative intelligence are likely more important now, given our complex world and unwieldy political systems, then they may have been when Jefferson was president. But writing may have been more important then as it was the primary medium through which people communicated. When attempting to actually quantify IQ, I see even more room for error. We simply don’t have the same number of data points in the historical record from which to compare, say, FDR’s intelligence to Washington’s.
I found an interesting blog post from 2006 in which Professor Thomas Reeves, author of biographies on John F. Kennedy and Chester A. Arthur, debunks the notion that presidential IQ can be measured.