I'll quote an old soc.history.what-if post of mine:
***
As I have posted previously about Lodge's decision to insist on
reservations rather than to oppose ratification outright:
"This involved an element of risk, since theoretically Wilson might accept
the reservations (and once that happened, Britain and France would accept
that having the US go into the League with reservations was better than
having it not go in at all). Senator James Watson (R-Indiana) in his *As I
Knew Them* recalled how he had actually raised this point with Lodge:
"'Senator, suppose that the President accepts the Treaty with your
reservations. Then we are in the League, and once in, our reservations
become purely fiction.' (Watson, like Borah and other irreconcilable
opponents of the League, thought that declaring that the US was not bound
by Article X unless Congress decided on the use of force would not amount
to much. Once the League's Council had voted to use force, with the US
delegate agreeing, Congress, he thought, would not dare refuse; to turn
down a President's request under such circumstances would greatly
embarrass the US before the world.)
"Lodge was not worried, replying with a smile, 'But my dear James, you do
not take into consideration the hatred that Woodrow Wilson has for me
personally. Never under any set of circumstances in this world could he
be induced to accept a treaty with Lodge reservations appended to it.'
"'But,' Watson retorted, 'that seems to me to be a slender thread on which
to hang so great a cause.'
"'A slender thread!' Lodge exclaimed. 'Why, it is as strong as any cable
with strands wired and twisted together.'
"Lodge was right--yet in a sense Watson was right, too. There *was* a
slender thread--Wilson's life. Wilson would never have accepted the Lodge
Reservations, but what if his stroke had killed him? Then the much more
flexible Thomas Marshall would have become President, and the combination of Wilson's
'martyrdom' and Marshall's willingness to accept the Lodge Reservations (or at least something like them)
could have made US membership in the League inevitable."
https://groups.google.com/d/msg/soc.history.what-if/9yi_qjHhwvI/tBRmrpo7XgsJ
***
In the same post, I also explain why I don't think US participation in the League will make much difference.
Anyway, even if the Treaty is approved with reservations (and Britain and France accept them, realizing that without the US, the League will be too weak), I still don't see Marshall being elected (not re-elected, since he was never elected *president*) in 1920. There will be too much resentment of the state of the economy, of the peace treaty (even if ratified on the ground that some peace treaty and League are better than none, few people are going to actually *like* it and some people and especially some ethnic groups are sure to hate it), of the War itself (and not just from people who had actually opposed the War when it was going on)--and basically of "Wilsonism" in general.
