If you could change one event in history,

[NNadir]

28. The powers at Versailles were not about to surrender their punitive approach to Germany...

...to Wilson whether or not he was clear headed.

The French, in particular, were extremely bitter over the loss of Alsace and Lorraine in 1870, had lost millions of men in the war, and had huge damage to their territory, where much of the fighting took place. (Parts of France are still essentially uninhabitable as a result.)

I consider Woodrow Wilson to have been the worst Democratic President of the 20th century, not because of Versailles - where he was not really in a position to dictate anything - but because of his virulent racism. This said, Versailles was not his worst failure; he spoke up for self-determination of European people, wasn't (as the French and British were) looking for spoils of war, and initiated a (failed) approach to an international body that anticipated the UN, which would come into being in 1944, which for all of its limited powers, has been an excellent international forum for defusing dire situations.

In the colonial mindset of the early 20th century, obtaining spoils of war was very much on the minds of the British and French and frankly there was nothing, nothing at all, Wilson could do about it.

When the war restarted in 1939, because of the application of mythology about the putative "stab in the back" lie of the Nazis, Roosevelt was in a far superior position than Wilson had been, and, in fact, Stalin was in a superior position to that of Lenin (who ceded huge portions of Russia to Germany at Brest-Litovsk).

In retrospect, given how things turned out half a century later, the best decision, aided ironically by Hitler's refusal to surrender, was to completely and totally militarily occupy Germany and to partition it until it was safe to reassemble that country after the Prussian mythology by which it was founded had rotted away in a subsequent generation.