Why has Harry Truman been rehabilitated?

[RINO Tom]

Andrew Jackson, Woodrow Wilson, Harry Truman and LBJ all hold a hilariously similar niche in Democratic history in that they were all unquestionably "progressive" for their times (in that they tried to enact legislation that they believed would help the needy and better society ... they just all had different definitions of who the needy were and who was deserving of their help, just as progressives still do today). 

Jackson pretty much committed genocide against American Indians (something the modern Democratic Party obviously doesn't want to associate itself with, rightfully so), so Democrats intentionally forget sometimes that he really did plant the seed for their party to be "The Party of the People."

Wilson was an unabashed racist and segregationist, and his internationalist worldview has fallen out of favor with the left in recent decades, so Democrats intentionally forget sometimes that his fiscal record of reform and regulation set the stage for FDR.

Truman's decision to drop the atomic bomb doesn't exactly jive with the anti-war left's worldview, so Democrats intentionally forget sometimes that he might have been the most fiscally liberal POTUS of the 20th Century and that he fought harder for progressive economic legislation than anyone not named FDR.

LBJ vigorously supported an internationalist war that history has decided was a failure (something the modern Democratic Party obviously doesn't want to associate itself with, rightfully so), so Democrats intentionally forget sometimes that his Great Society programs have more or less served as the basis for Democratic fiscal thought since then.

Out of those four, Truman and LBJ are definitely the closest to being re-embraced.  Wilson is third, and Democrats have largely abandoned their founder.