Liberal historians of American politics have long held, at least implicitly, a teleological view of our history. The assumption is that America is slowly moving toward a more “progressive” (read: statist) society, and the only thing the right can do is slow the movement. Conservatives cannot stop or reverse it–it is inexorable.
This helps explain the consistent biases of historians’ presidential rankings, for instance, why Woodrow Wilson is regularly ranked in the top ten but Calvin Coolidge is mired in the high 20s. Wilson advanced the “liberal” project, and therefore he is promoted. Similarly, presidents with serious, oftentimes damning downsides – notably Harry Truman and Lyndon Johnson – are ranked higher simply by virtue of having pushed the progressive ball forward.
