Nothing, according to Gary Becker: 

President Obama, in his State of the Union address, advocated special tax breaks and support for the manufacturing sector. I do not see any more convincing case for subsidies to manufacturing than there was for the special treatment of agriculture during the long decline in farm employment. Most of the arguments made in support of privileges for manufacturing could be made for services and other sectors of the economy.  

Richard Posner seconds him:

Employment in agriculture has plummeted, leading to anxieties spurred by agricultural companies about the decline of the “family farm” and the loss of the imagined virtues of the independent farmer, to combat which agriculture continues to be heavily subsidized. The subsidies are widely recognized to be a pure social waste, and the same would be true of subsidizing manufacturing. Like manufacturing, American agriculture is thriving with its historically small labor force.