I think the question is how do you get a isolationist dove in the White House?
We tend to forget that the Al Smith presidency of 1929-1933 was isolationist and the Hoover Administration of 1933-1945 engaged the world to fight the depression. Hoover was just not going to allow the "atrocities" in China to go unpunished.
I think we need to consider the possibility of an isolationist movement being stronger as opposed to a "combined trade" agreement. In the long haul, we are far better off with Hoover dropping Smoot-Hawley and lanching a massive trade program with Germany--can you believe that Hitler got 30% of the vote?
In short, Japan had gone nuts, and they were going to hit US assets in China, and no matter what happens, President Hoover would never allow it to work. So, there is no way that war would be avoided with Japan unless the Japanese or the USA were more dovish.
The United States has been a friend of China for decades; it will not allow its friend to get chewed up by the Japanese.