Truman started life with few economic resources, served in many local government positions, saw combat in World War I. As president he implemented the Marshall Plan, promoted civil rights and a national health insurance program.
Born a millionaire, Trump faked a bone spur to avoid the draft, cheated contractors, cheated on his taxes, hired undocumented immigrants while placing the children of asylum-seekers in cages, thinks NATO is a joke, is dismantling the Affordable Care Act, and violated the Constitution by bribing/extorting an ally, Ukraine, at war with an adversary, Russia, for personal gain.
So why is this misunderstanding important? If you don’t know history you will confuse cause and effect. In the 1920s and 1930s, the tyrants of Europe didn’t just suddenly take power. They were elected by a frustrated and confused electorate promulgated by lies and misinformation and by parliamentary representatives that abdicated their responsibility and allowed fear and scapegoating of “the different” to become the core of their government.
Getting back to Harry and Donald, it seems that the only thing they have in common is the first letter of their last name.