Industry Week has a great scholarly article showing how the decline of manufacturing through relentless offshoring and trade agreements has caused US income inequality to rise to 3rd World levels.
It is a long article, but well worth the read.
It shows how the rise of manufacturing in the Post World War II era, with job intensive industries and good pay, lowered US income inequality to record low levels. Conversely, it shows that the modern trade agreement era, from 1974 to present, gave rise to "relentless offshoring". Manufacturing as a percentage of the national economy headed downward. Income inequality in the US became worse than most other developed countries.
Any Obama or GOP policies designed to create jobs and income in the US simply cannot succeed with the TPP and similar trade deals that cause massive goods trade deficits.