President Trump sees it as a zero-sum game for the auto industry. The administration wants very aggressive changes to rules of origin with domestic content requirements, meaning some of the car must be made in the US to qualify for USMCA, and almost none should be made with Chinese components. This protects the North American industry from Chinese inputs.
It's a negotiation, so we'll see where this lands, but the goal is to bolster the domestic industry and protect against Chinese inputs.