BTW, the proposed treaty of guarantee had a lot of wiggle room:
https://history.state.gov/historicaldocuments/frus1919Parisv13/ch27
"In case the following stipulations relating to the left Bank of the Rhine contained in the Treaty of Peace with Germany signed at Versailles the 28th day of June, 1919, by the United States of America, the French Republic and the British Empire among other Powers:
“Article 42. Germany is forbidden to maintain or construct any fortifications either on the left bank of the Rhine or on the right bank to the West of a line drawn 50 kilometres to the East of the Rhine.”
“Article 43. In the area defined above the maintenance and assembly of armed forces, either permanently or temporarily, and military manoeuvres of any kind, as well as the upkeep of all permanent works for mobilisation are in the same way forbidden.”
“Article 44. In case Germany violates in any manner whatever the provisions of Articles 42 et 43, she shall be regarded as committing a hostile act against the Powers signatory of the present Treaty and as calculated to disturb the peace of the world.”
may not at first provide adequate security and protection to France, the United States of America shall be bound to come immediately to her assistance in the event of any unprovoked movement of aggression against her being made by Germany."
https://history.state.gov/historicaldocuments/frus1919Parisv13/ch27
If the US wats to avoid war in 1939, it can simply say that Germany had not yet made any "unprovoked movement of aggression" against France (as opposed to Poland). So the US is perfectly free not to go to war...