Hughes would likely have taken the US into WWI. Unlike Wilson, he would likely have gotten the League of Nations Treaty ratified.
Part of that would have been because Hughes would not have had a debilitating stroke. Part of that would have been because Hughes would not have killed the treaty over partisan considerations.
What many people don't seem to realize is that it was WOODROW WILSON that blocked the ratification of the treaty. Henry Cabot Lodge (whom Wilson hated on an intensely personal level) got the GOP to attach a number of "Reservations" to the treaty. The "Reservations" didn't amount to a Hill of Beans, but they were, as Prof. Thomas Bailey observed, a Republican wrapper to Wilson's loaf of bread. Wilson wanted a Democratic wrapper, and he instructed Senate Democrats to vote against the Treaty. When it was killed, Lodge refused to bring it up again.
Charles Evans Hughes would have not let such considerations get in the way of ratification of the treaty. He would have made his peace with the isolationists in his own party. Indeed, this accomplishment would have mitigated the harsh peace terms imposed on Germany which led to the sort of resentment that led to the rise of the Nazis and Hitler. And Wilson's stubbornness was exacerbated by his stroke. Hughes would not have had that problem, either.
Hughes would have been elected by the solid margins Republican Presidents were re-elected back then.
A quick read on wikipedia, and the Lodge reservations was basically what the US has with the UN today
1. The US can leave the League for any reason regardless of prior obligation
2. The US has no obligation to defend another nation's integity even with a League vote
3.The US has no obligation to administer mandates like Syria or Nambia
4. The US has sole judicial juridiction over its land
5.The Monroe Doctrine must still exist
7. Congress must vote on the US rep to the League
8. The US will control its trade with Germany
9. The US has no obligation to pay money to the League
10. The US has no obligation to limit its military
11. Citizens of other nations that break the League's rules can live in the US
13. If the League forms new organizations, the US doesn't have to join
