Abraham Lincoln faced the breakup of the Union and the Civil War in his Presidency from 1861-1865.
Franklin D. Roosevelt faced the Great Depression, the growing threat of Fascism and Nazism, and World War II, from 1933-1945.
Other than Lincoln and FDR, the question arises which other Presidents faced crises on a level as dangerous and challenging as those two Presidents.
One could say George Washington facing the challenge of making the Constitution work, and the nation able to survive as a republic from 1789-1797.
One could say Harry Truman, facing the challenge of sudden elevation to the Presidency in a time when World War II was not yet resolved, and having to deal with the threat of the Soviet Union during the Cold War years from 1945-1953.
One could say John F. Kennedy, facing the threat of the Soviet Union, including the Berlin Crisis and the Cuban Missile Crisis, which dominated his time in the Presidency, from 1961-1963.
One could say George W. Bush, facing the challenge of the terrorist attack on September 11, 2001, and the dual wars fought during his Presidency in Afghanistan and Iraq, and the Great Recession which developed in his last year in office, from 2001-2009.
One could also say Barack Obama, facing the challenge of the Great Recession, the worst economic downturn since the 1930s, and the constant domestic resistance from the right wing Tea Party Movement, and the growing extremism of the Republican Party, from 2009-2017.
But one could also argue that Joe Biden, facing the COVID 19 Pandemic; the growing epidemic of mass murders by firearms by domestic terrorists and mentally disturbed people; and the threat of nuclear war in the midst of the greatest foreign policy crisis (The Russia-Ukraine War) since the Cuban Missile Crisis of 1962, is the greatest challenge and crisis other than Lincoln and FDR!