During 1914-16, the vast majority of Americans wanted to stay out of the war, as did Wilson. He genuinely thought he could do so, and was very lukewarm toward the Preparedness Movement. Wilson's patient efforts at trying to solve things by diplomacy rather than war continued even after the Lusitania sinking, efficient Allied propaganda within the USA, actual German "atrocities" like Edith Cavell shooting, German sabotage in America, and the Zimmermann Telegram had certainly convinced the vast majority of Americans that war was now the only option. Once Wilson had decided war was inevitable after the resumption of unrestricted submarine warfare by the Germans in February 1917, he was able to carry with him an (almost) united nation.
My debate is with the underlined portion. I'm not convinced the evidence that the vast majority of Americans thought war was the only option. My reading of the evidence is that most Americans remained unwilling participants in the war, but that they went along with government policy because that's what they do. The idea that there was a strong anti-war movement that possibly reflected a plurality passively opposed to the war just doesn't fit with our National Myth of America's progress to Superpower Status, which replaced our original, more isolationist, National Myth. I'll publish what I've found over the next few days, together with any new stuff I uncover as well.