Democratic legislators are systematically more likely to support the liberalization of migration policies than their Republican counterparts, while the opposite is true when it comes to trade policy.
From the paper "The political economy of trade and migration: Evidence from the U.S. Congress" by Conconi, et al (December 2012).
From the abstract:
. . . Representatives from more skilled-labor abundant districts are more likely to support both trade liberalization and a more open stance vis-`a-vis unskilled immigration. Still, important systematic differences exist: welfare state considerations and network effects have an impact on the support for immigration liberalization, but not for trade . . .
HT: Eugene Beaulieu