You might wonder why Democratic mayors would disagree so strongly with their counterparts in Congress. Here is Brownstein's answer to that:
New data released May 13 by the Brookings Institution's Metropolitan Policy Program helps explain the mayors' tilt toward trade...Brookings found that fully 86 percent of U.S. exports now originate from urban areas. Moreover, exports drove more than one-quarter of all metro area economic growth from 2009-2014. "This has metro leaders and elected officials placing an increasing focus on exports as a way to grow and maintain their regional economies," said Bruce Katz, the Metropolitan Policy Program's codirector, in an email. In their letter to Senate leaders, Johnson and Rawlings-Blake indicated the conference's own forecast projects that exports will account for one-third of metro areas' economic growth in coming years...Brownstein goes on to point out the shift in public opinion on trade.
Democrats now control the mayor's office in 18 of the 20 cities that anchor the metro areas that Brookings found derive the most jobs from exports. (The only exceptions are Republicans Kevin Faulconer in San Diego and Tomas Regalado in Miami.)
The unexpected result is that a series of recent surveys have found that Democratic partisans now express more support for free trade than rank-and-file Republicans—inverting the historic party stereotypes. In last month's national NBC/Wall Street Journal poll, a 43 percent to 26 percent plurality of Democrats said that free trade has done more to help than hurt the United States, while Republicans narrowly split in the opposite direction (33 percent said it helped, 36 percent said it hurt)...All of this suggests that the views about trade in the general public are much more complex than how they are typically stereotyped in the media - as well as the current battles over TPP in Congress.
The change also reflects the Democrats' diminishing electoral reliance on blue-collar whites generally dubious of free trade and their increasing dependence on both the college-educated whites and minorities who are more open to it.