“They’re not going to war with Japan,...”
They may act like they want to - but are still very afraid of the Japs (and agree - Japs will ally w/ Vietnam and Philippines - with a very interested India on the sidelines).
Meanwhile, Japan has been an ally of the US at least since the defeat of the Nationalist Chinese... Look how 0 has turned on other allies and sucked up to former adversaries.
Plus, we owe the chinese lots of money. The way they see it is we're not really in a position to complain about their conduct.
Oh, and those other countries that we'd wish to see allied with Japan? South Korea, Vietnam, the Phillipines? (Thailand, Singapore, India?) They too have a sense of history that goes back before Nanking. They'll look the other way, just as we will.