This is interesting. Brad Plumer crunches some numbers and finds:
Let's look at some actual poll numbers, namely, the recent and massive Pew Press poll that divided voters up into different subgroups. On the question of whether trade agreements are "bad for the U.S." or "good for the U.S.," the only core Democratic constituency that's overwhelmingly in favor are "liberals," 50-44 percent. Needless to say, they're not in any danger of leaving the Democratic party. Meanwhile, the two other core Democratic groups—"Disadvantaged Dems" and "Conservative Democrats"—are much more tepid on trade agreements.
More than anything else, this seems indicative of how the party now judges liberalism. Contemporary Democratic liberalism isn't much of a populist exercise: it's social liberalism, dovishness, and support for enhanced government intervention in the economy. It's not redistributive, it's not particularly focused on the worker, and it's not particularly responsive to their concerns. It's the sort of liberalism that a fair fraction of educated folks reach after a certain degree of study and exposure to the party's intellectual organs. That's why a number of our former supporters have peeled off into the GOP camp, becoming what Pew calls pro-government conservatives.
That's not necessarily a criticism. Protectionism is a bad thing, as are antigrowth policies, nativism, and many forms of redistribution. Indeed, too much of a focus on the worker's concerns can lock in the status quo, preventing progress in all sectors of society. But Democrats would be well-served to figure out how to make their favored form of liberalism more resonant among the people it's supposed to benefit. We keep losing powerful majorities of working class white folk to the Republicans and finding that our party's left wing supports supposedly worker-friendly policies that workers find fairly unfriendly. Policies that are obviously beneficial to certain segments of the Democratic coalition are looking completely inexplicable to other portions. That needs to change. Fighting Republicans on CAFTA hard enough to separate our support of fair trade from their advocacy of free (and decidedly corporation-friendly) trade would be a good place to start.