The best "uniters" in recent decades were also the best dividers: FDR, LBJ, RMN got the country to line up on their side by making the other side look so awful that there appeared to be no alternative.
That popularity didn't last for Johnson or Nixon, any more than the high popularity of the Bushes in 1991 or 2001 lasted.
Theodore Roosevelt was probably a "unifier." He managed to win over both sides of the political spectrum and leave only voters who couldn't vote Republican because of ethnic or regional loyalties out of his camp. You couldn't do that in our highly ideological era.
Eisenhower was also probably a unifier, because he essentially won the Presidency by winning the war years before. Even a lot of the people who voted against him weren't really against him. That doesn't happen today either.
John Kennedy was a partisan divider who slammed the Republicans every chance he got in 1960. But he inherited much of the good feeling of the Eisenhower era and ended up being more popular than he probably deserved. Getting shot helped.
RE: “John Kennedy was a partisan divider who slammed the Republicans every chance he got in 1960. But he inherited much of the good feeling of the Eisenhower era and ended up being more popular than he probably deserved. Getting shot helped.”
***********
Agree — post-war Eisenhower era was full of good feelings and new prosperity and Kennedy inherited that, plus people thought JFK was young and had a good looking family et al. By today’s standards, Kennedy was not very far “left” at all.
And yes, the assassination so early in the presidency, before the honeymoon phase had time to be over, helped his legacy more than anything.