In that lecture linked below, Frankel has some other observations too, and lays down the oft-heard line that the two parties have swapped economic policies over the years: "Republicans have become the party of fiscal irresponsibility, trade restriction, big government, and bad microeconomics." While Democratic presidents have advocated mostly the opposite.

Fair enough, though he doesn't quite explain the shift (it's a tiny data set in any case). On trade, for instance, I think George W. Bush is at least as committed to free trade as either Bill Clinton or, say, John F. Kennedy was. (Yeah, yeah, people bring up the steel tariffs, but the way I see it: after watching Clinton cost Gore the 2000 election by refusing to impose those tariffs, any president would have been stupid not to throw them down in 2002.) But Bush's trade agenda is constrained by two things: First the jobs situation has mostly languished since he entered office, and whether that's his fault or not, it's made free trade a much, much tougher sell; and second, Bush hasn't made any effort to lend a hand to those who lose out from globalization—trying to kill the Trade Adjustment Assistance program didn't help much.

That makes the politics of trade thorny, and they were thorny for Bush from the start—as a post-election Democracy Corps poll found, "Bush voters who had seriously considered Kerry are hostile to NAFTA by a two-to-one ratio." But it's not just swing voters: white rural voters, older voters, and non-college educated males are all overwhelmingly hostile to NAFTA. That's the Bush base right there. Also, I don't have a cite, but I seem to remember Greenberg making the point somewhere that white evangelicals were pretty lukewarm on NAFTA too. (So why did they vote for Bush anyway? Part of the reason might be that only 13 percent of his supporters correctly understood the president's position on trade.) In fact, it wouldn't be too surprising if most of the grassroots-ish support for freer trade could be found among non-union Democrats. Note that opposition to CAFTA is actually stronger in red states than in blue states—presumably because it would affect farmers and textile workers the most, but perhaps for demographic reasons as well.