There are always two camps of people in this debate. One camp says the medical expense and overhead dealing with regulations and union are too costly to operate manufacturing entirely in the US. There is another camp that says the cost operating oversea (training staff, relocating senior staff oversea, legal and book keeping management) is close to operating in the US.
Fact is many companies are now moving away from China, and are signing up new manufacturing sites in other Southern Asian countries such as Thailand and Vietnam for lower operational cost (note a lot of the U.S. companies give contract to oversea manufacturer, so it is these manufactures moving away from their own domestic sites - for example, Foxconn being a largely a Taiwanese company Foxconn manufactures outside of Taiwan).
I don't know how close operating in the US vs operating half of the business offshore is. This is like hiring consultant oversea for software development. The first burden is operational efficiency; it is painful to manage oversea when you want your "brain power" to be in the US. For example, project manager might have to get up early say 6-7 AM to do a stand up and then follow up at 9/10AM (because your business owner / product owner don't get up at 6 to talk about progress). If there are bugs that need to be resolved during US hour, you still have to pay the extra hours. You are wasting time going-back-and-forth because your offshore team will get off work when you want to fit a meeting in the afternoon.
While most Chinese workers do not form union (fear of repucation), workers do come out and protest from time to time (see Foxcoon strikes). Local laws also do not often favor US companies, and local laws can be a pain in the ass.
The only thing I can think of that will keep some companies manufacturing outside of the U.S. is that these companies simply do not have cash in the US. Imagine a company like Apple (Apple has like 90% of its cash outside of US) the only way they can spend that money is do stuff outside of US.
This is just my uneducated opinion, having little idea how business and economy works. I am all for moving closer to proximity. If you are selling in the U.S. it makes sense to manufacture her. This is why many manufacture sites are now built in Mexico (looking at car makers). Shipping cost have been reduced in the last two decades because now we have bigger ships, but still, there is a schedule that you need to maintain.
Another classic example where some part of "making" are likely done domestic (or a place where known for using advanced technology) is the classic X ThinkPad series. The agreement Lenovo have with IBM is that the main design is to remain in a Japanese lab AFAIK. I am sure Lenovo has way to do stuff in China and do stuff in Japan, and still claim stuff are done in Japan. But branding is a good motivation for keeping certain things local.