From 1970 until 1998, U.S. manufacturing output fell from 23.6 % to 16.6 % of total GDP. However, this type of decline was worldwide, with world manufacturing output falling from 26.5 % to 18.8 % of total world GDP. During that time, apart from the adjustments of the mid 80's, U.S. manufacturing was faring about as well as the rest of the world.
Starting around 1998, there was a sharp decline in U.S. manufacturing as compared with the world. U.S Manufacturing as a share of GDP fell 20 % (16.57-13.29) from 1998-2007 ; for the world, it fell 10 % (18.81-16.90). Bubble-nomics in the U.S. enabled the weakness in manufacturing and its support industries to be masked.
The Plaza Accord, in 1985, dealt with the last such drop in U.S. manufacturing by orderly devaluing the dollar. This is evident on the chart. After the finance implosions of 2008, it will be difficult to ignite a new bubble in the private sector. Basically, the dollar is overvalued relative to the manufacturing strength of the United States.
Other thoughts: China's influence is part of the story post-1998. How much that has to do with a depressed Yuan, versus productivity issues (such as wage arbitrage), is hard to say.
The dropping of the gold standard in the early 70's also acted as a type of devaluation, going into the mid-70's.
Source is here, stats here.