on a more subtle scale, Woodrow Wilson got the flu in 1919, which apparently made him paranoid and exhausted him, possibly contributing to him conceding to Clemenceau's demands for The Treaty of Versailles which in turn contributed to some Not So Good things down the line

from this new yorker article

During the second week of April, an exhausted Wilson gave up most of the demands that he had been pressing Clemenceau to meet. The President accepted the demilitarization of the Rhineland and its occupation by France for at least fifteen years, along with an open-ended process for calculating Germany’s reparations bill. In the judgment of Margaret MacMillan, the author of “Paris 1919: Six Months That Changed the World,” an authoritative account of the postwar negotiations, Clemenceau suddenly found himself with “the best possible deal for France.” Infamously, the achievement was a Pyrrhic one. The Treaty of Versailles, signed on June 28, 1919, and which ratified Wilson’s concessions, proved to be a settlement so harsh and onerous to Germans that it became a provocative cause of revived German nationalism during the nineteen-twenties and thirties, and, eventually, a rallying cause of Adolf Hitler.

Barry considers in his book whether Wilson might have been a more forceful and stubborn negotiator in Paris if he hadn’t contracted the flu, and whether, therefore, the history of the twenties and thirties in Europe might have turned out differently. He is appropriately skeptical of such counterfactual speculations; we cannot know what might have happened if Wilson had remained healthy and vigorous, only “what did happen,” as he writes. “Influenza did strike Wilson. Influenza did weaken him physically. . . . precisely at the most crucial point of negotiations.” Nazism’s triumph over Germany was caused by much more than the blowback from the Versailles Treaty, yet there can be little doubt that the treaty’s punishing terms, including the highly visible French occupation of German territory, did help Hitler to mobilize and narrate German grievances. Lloyd George, who had opposed, in particular, the French occupation, later concluded in a memoir that the “odious accompaniments of such an occupation of German towns . . . had much to do with the fierce outbreak of patriotic sentiment in Germany, which finds its expression in Nazism.”

then Wilson got a stroke 6 months later

also not a pivot but in an extraordinary coincidence both Adams and Jefferson died on July 4th 1826