1. JOHN F KENNEDY (Whose tragic murder gave the nation LBJ/Vietnam/Unnatural Dem Congressional Majorities in 1964 and the resulting catastrophic ‘Great Society’ and Third-World-open-door immigration bills), and
2. THEODORE ROOSEVELT (Because he was a shoo-in for the 1920 GOP nomination and another term as president).
I could come up with more names, but these two were obvious. The reason for the order is that another term of TR would not have changed the nation’s future much for the better (in fact, it may have been significantly worse that the Harding/Coolidge presidency as Coolidge is one of our most underrated presidents).
JFK’s murder was a real tragedy for the nation. Weak as he had been in dealing with Cuba and the Russians, he was unlikely to have dragged us into Vietnam (he listened to Gen Douglas MacArthur’s repeated advice to stay the He** out of a land war in Asia in their several meetings and quoted it to his cabinet members often), plus he was the last national Democrat who truly understood, appreciated and approved of Capitalism.
Even his slow movement on the liberal icon of the ‘Civil Rights Movement’ is, I would argue, a positive thing in our review of history, as slower pace of social change is always - ALWAYS - less disruptive to a nation that a pell-mell rush forward ...
JFK was the one who originally pushed those Third-World Open Door Immigration Bills.
Speaking from family experience John Kennedy was not remotely interested in bugging out of Vietnam. He had 16,000 American personnel there and was increasing our involvement right up to the time of his death, even promoting the coup that killed President Diem in order to give Kennedy more control over Vietnam’s internal policy. The chaos resulting from Diem’s assassination was dumped on Lyndon Johnson, who managed to make a bad situation worse.