Comment by anovikov
Moreover, share of GDP has been falling because prices of manufacturing goods have been all falling vs inflation, pressured by foreign competition and by productivity improvements, while rest of the economy - services - face none of that: they usually (except corner cases like call centers) can't be outsourced abroad, and output there depends strongly on labor inputs (e.g. waiters) thus making productivity stagnant almost by definition.
So there isn't a problem about manufacturing, never has been. Problem is strictly about manufacturing employment, which is of course, inexorably falling and will continue doing so and every politician promising to reverse it is a blatant liar. It's falling much like farm employment has been falling 40-70 years ago, sure it's traumatic, ruins livelihoods of millions of families many of which will never recover, destroys not just their personal finances but their source of pride and sense of self in many ways. But just like it didn't result in decrease in food output back then (quite the opposite happened), it doesn't result in dearth of manufacturing products now.
You could outsource more services and automate them more. But many service industries are protected by laws and regulations from such competition and improvements.