Maybe with Wilson dead Italy can get more at Versailles...
First off I agree that Marshall gets a compromised Treaty of Versailles passed by acceding to GOP reservations.
This however probably changes things down the line. With the Senate accepting even a modified version of the ToV, fervent isolationism is going to be less of an option with the GOP. This means that the GOP isn't going to pick Warren Harding and probably will pick someone else (Wood?). That in and of itself could drastically change things in the interwar period potentially butterflying away the Great Depression.