"worst" and "horrible" are subjective words. Least liked? Perhaps.
Worse:
Firebombing Dresden (Roosevelt)
Nuking Japan - Twice (Truman)
Destabilizing the middle-east and ruining Iran's democracy (Eisenhower)
Throwing Americans into a war they wouldn't win in Vietnam (Johnson)
US-Led Sanctions that killed over 500,000 Iraqi Children (Clinton)
Displacement and death of over 13 million Syrians (Obama)
More horrible:
Massive spying, rigging, and bugging of political opponents (Nixon)
Accepting an extra-marital affair so that you can keep Clinton's last name to advance future polital career (H. Clinton) and being implicated in multiple corruption scandals.
Possible involvement in defense contract bribery, while acting president (Bush Jr.)
And the worst thing Trump did was.... use Twitter...?
Be fair in your judgement.