'Why Have Americans Become More Positive About Trade?'

Anyone have an answer?:

Why Have Americans Become More Positive About Trade?, by Erik Voten: A recent Gallup Poll has found that Americans have become remarkably more positive about foreign trade. Below is the key graph:

This is a pretty major shift that could bode well for President Obama’s announced plans for a new transatlantic trade deal and the Trans-Pacific Partnership. So why such a big shift? ...

[T]here is also a partisan story to be told here. Back in 2009, 43% of Democrats and 45% of Republicans saw trade as an opportunity for growth rather than a threat to the economy. In 2013. this is 66% of Democrats and 51% of Republicans.  In other words, most of the change has come from Democrats following President Obama’s prominent endorsement of new trade deals in the State of the Union address. ... Democrats are now 15 points more favorable towards free trade than Republicans in this poll.

Another fascinating difference with 2009 lies in the income breakdowns. In 2009, 52% of those making more than $75,000 were positive about trade versus only 35% of those making less than 35%.  In 2013, these numbers were 57% and 54% respectively. ...

The patterns are pretty similar if you look at liberal/conservative rather than party identification and education rather than income. ... The question to ask is thus why so many Americans who identify as Democrats (and liberals) and so many Americans with low incomes and/or little education have become more positive about trade?