Simple raw calculations are all that is needed to determine which president was the economically pivotal presidency. Finding out that Herbert Hoover was economically pivotal comes as little surprise to those that never fell for his false reputation as a do nothing president.
Reading "Recarving Rushmore" by the Ivan Eland of the Independent Institute gives an interesting perspective to a usually overlooked president, William McKinley. It is commonly assumed that he wished to avoid war with Spain, but research by Ivan Eland shows otherwise. William McKinley played a very coy game of pretending to oppose the war while encouraging it behind the scenes.
While previous wars had some sort of arguable pretext, even though in the Mexican-American war the actual course of the war went far beyond the pretext, there at least was a case to be made for military action by the United States. There wasn’t always a good case, but there was some case.
The case for the Spanish-American war was imperialism, nothing less and nothing more. The sinking of the Maine served as an incident, but didn't serve as a cause. More than any other military action, it set the course for future United States military involvement around the world, setting the state for the many crimes of Woodrow Wilson.
The reason why William McKinley doesn't get the recognition he deserves is because while preparing for war, advocating war, and later waging war, his public statements were to the effect of opposing war. Why he spoke out against a war that he wanted is a very curious subject to examine, which can be read about in "Recarving Rushmore."