A lot of people would instinctually say Abraham Lincoln, but—to me—I have a hard time really calling Lincoln’s Presidency “great” since it’s the first and only time America had a Civil War, and it occupied his Presidency from start to finish.
The South started seceding before Lincoln even took office, and the final Southern troops surrendered after Lincoln was assassinated (Lee’s surrender at Appomattox were not the last Southern troops to surrender).
It’s just really difficult to judge his presidency at all since the circumstances were so unusual. You might also argue that Lincoln didn’t effectively fight the Civil War since it lasted several years longer than anyone thought it would.
The other 44 Presidents did not have a Civil War occupying their Presidencies from start to finish, and it’s much easier to judge them…
Having said that: most Republican Presidents have been awful. And I mean awful (Hayes, Grant, Taft, Harding, Hoover, Nixon, Reagan, Bush, Trump).
It’s amazing people are still voting for them since Democrats haven’t had a truly awful President since the days of Andrew Johnson or James Buchanan, but Republicans have had 10 or so since then.
But there have been exactly two great Republican Presidents: Teddy Roosevelt and Eisenhower.
Although, Roosevelt eventually formed the Bull Moose Party to challenge his ex-VP Taft, and that is the first time in history an ex-President has ever left their own party to run again.
And Eisenhower would doubtlessly be considered a “RINO” today and kind-of was even back then. The Koch Brothers’s father Fred Koch (a major industrialist and figure in the Republican Party, in addition to co-founder of the John Birch Society) thought “Ike” was a Communist. And Eisenhower was constantly having to butt heads with Senators like Robert Taft (President Taft’s son) and Joseph McCarthy.
In truth, most Republican Presidents have been absolutely terrible and left office in disgrace (Nixon, Hoover, Reagan, Harding, Bush, Trump), and then had their image rehabbed over time. And that’s why people keep forgetting how bad they were, and keep voting for the next one.
Within the Republican Party, Eisenhower is not fondly thought of at all because his tax rates were so high, and he was the most pro-working class President they’ve ever had.
And even though people wrongly attribute the fall of Communism to Reagan, it was actually Eisenhower who helped carry on the plans of Harry Truman (United Nations, NATO, the Korean War, containment) that built the international order that would be the Soviet Union’s ultimate undoing.
And Eisenhower managed to do this without creating most of America’s major enemies unlike Reagan (Iran Contra affair, inadvertently building the Taliban and Al Qaeda in Afghanistan, making deals with China and cutting arms shipments to Taiwan, abandoning Lebanon to fight in Grenada, making deals with drug traffickers to fund the anti-Communists in Latin America).