This is the bottom line on American manufacturing:
> From 2000 to 2010, the United States lost some 5.6 million manufacturing jobs, by the government’s calculation. Only 13 percent of those job losses can be explained by trade, according to an analysis by the Center for Business and Economic Research at Ball State University in Indiana. The rest were casualties of automation or the result of tweaks to factory operations that enabled more production with less labor.
> American factories produced more goods last year than ever, by many indications. Yet they did so while employing about 12.3 million workers — roughly the same number as in 2009, when production was roughly three-fourths what it is today.
Most of the jobs that left are never coming back. They didn't go to Mexico or China; they simply disappeared because automation and productivity increases rendered them unnecessary.
If the US sheltered its manufacturing sector from foreign competition, a small number of jobs might come back, but the increased cost of manufacturing things in the US would strongly incentivize companies to automate those jobs away as quickly as possible.
Manufacturing has a powerful political resonance, both in terms of the imagery of hardworking middle-class factory workers and national pride, e.g. "Why don't we make things in this country anymore?" However, I suspect that most politicians who talk about a manufacturing revival understand that it won't really happen.