The peacetime supply chain determines the possibilities of the wartime supply chain. You can't open a mine overnight, refineries are incredibly expensive and fiddly and require a lot of very specific knowledge, tool manufacturing capacity is incredibly difficult to bootstrap- you don't want to be like WWII Australia, digging up lathes out of junkyards.

America doesn't have the manufacturing base it had in WWII. Then, it took months or even years to ramp up the existing manufacturing to wartime capacity. Now a lot of America's manufacturing has been outsourced to China and other far eastern/southern Asian countries. A modern war between superpowers is likely to be won or lost in a week or two at most even without involving nukes, long before major resupply of equipment is even needed.