2015 - intel/ms produce all goods in China - the computer sent to the US
2020 - intel/ms declare bankruptcy. Chinese companies produce all parts and software, computer sent to the US
The problem is not just the assembly cost, which is in fact marginal. The problem is the costs all down the supply chain. All the components inside, say, an Ipod are made in China. All the profits made producing and selling those items stay in China. I don't think you could even produce a computer in the US today. You'd have to get and ship all your parts from Asia. Hard drives, memory, displays, discrete components - all made overseas. The huge support base for producing all electronics have moved overseas. If a $200 Ipod costs Apple $150 in parts, $10 assembly/packaging/shipping and $40 profit, that's still $150 that flowed into Chinese economy - not the US economy.
Prototyping and design used to be done here. It's now easier to get the engineering talent overseas where engineers have access and contact with the people producing the actual parts they need to use in their own products. We've lost the production capability, we're about to lose knowledge about how to even create the devices we invented.