I've read a ton of his posts, so I can attempt to summarize. It's not money in general that was running out in 1917, it was the ability to pay for American goods, oil and steel especially, though I imagine food and other odds and ends as well. To pay for those, you'd need either gold or dollars. The latter could be acquired through loans, but lenders usually want to be secured by collateral. Before entering the war, the Wilson Administration advised against banks giving unsecured loans to the Entente, so by early 1917 they were running out of gold, dollars, and American assets to use as collateral for loans. Should America have sat out, you'd see a drop off in American exports for lack of ability to pay, and without those raw materials, the war effort suffers badly, to the point where the Spring Offensive of 1918 probably can't be stopped-if they last that long.