If I had to name the most underrated president in American history, Warren Harding would be at or near the top of my list. Harding is routinely ranked at or near the bottom in presidential ratings by historians and other experts.
In Sunday's New York Times, Yale historian Beverly Gage has an interesting article suggesting that Harding may have been the first "black" president in the sense that it is possible that he had a remote black ancestor. Unfortunately, Gage's article about Harding and race relations completely ignores the fact that Harding made a well-known speech advocating full legal equality for southern blacks in 1921, in Birmingham, Alabama. As W.E.B. DuBois pointed out at the time, Harding went farther in advocating equal rights for blacks than any other post-Reconstruction Republican president (the Democrats, at that time the party of southern whites, were even worse). Indeed, no president went as far as Harding in advocating equal rights for southern blacks for several decades thereafter. Harding also lobbied hard for a federal anti-lynching bill to curb the rampant lynching of blacks by whites in the South - again, the first post-Reconstruction president to do so (the bill passed the House, but died in the Senate due to the threat of Democratic filibusters). As DuBois pointed out in the linked article, Harding was not wholly free of the racism common among whites at the time. But he was a lot better than the vast majority of his contemporaries.
Nor were these Harding's only positive aspects. As Gene Healy discusses in his interesting recent book, The Cult of the Presidency, Harding is also notable for reversing the severe violations of civil and economic liberties that had proliferated under his predecessor Woodrow Wilson. It's easy to belittle Harding's campaign slogan - "Return to Normalcy." But Harding's notion of "normalcy" included an end to the imprisonment of political dissenters (such as Wilson's notorious "Palmer Raids"), abolition of wage and price controls, and the reversal of Wilson's numerous illegal seizures of private property. As David Bernstein and I briefly discuss in this article, Wilson's administration was also highly racist and segregationist even by the standards of the day; here too, Harding was a sharp contrast.
I'm not arguing that Harding was a great president. His administration included some serious corruption (such as the famous Tea Pot Dome Scandal), and his intellectual and political skills were not especially impressive. And, as with most politicians, his successes were to a large extent the product of broader political trends, not just his personal efforts. However, Harding's achievements in ending Wilson's harmful policies and his laudable efforts on behalf of civil rights greatly outweigh the relatively limited harm caused by his corrupt underlings. And, by all accounts, Harding himself was clean (though many of his appointees definitely weren't).
Harding will never be ranked among the top few presidents. But he deserves much greater respect than he gets.