In May 2005, I wrote:

After the 2004 election I had this idea that Bush’s victory over Kerry is analogous to Truman’s over Dewey in 1948. . . . A key issue in the analogy, I suppose, is the implicit suggestion that Bush in 2005-2008, like Truman in 1949-1952, could see a continuing decline in approval followed by a loss in his party’s control of Congress.

Bush’s popularity has sometimes been compared to Nixon’s, but I think Truman’s a better comparison because it is gradual rather than the result of a single scandal.