Early Republicans, like the Whigs before them, stood for tariffs, not trade:
In the the 19th century the Democratic party, rooted in large part among Southern planters who were dependent on exports of commodities and imports of finished goods, was the party of free trade. The northern Whigs, and later the Republicans, were the party of tariffs. They were the faction which drew support from the industry of the North which benefited from protection against European competitors. The Republican support for tariffs and Democratic opposition persisted into the early 20th century. Only after World War II did this long standing division between the two parties diminish, so that by 1993 a much larger proportion of Republicans than Democrats supported the ratification of NAFTA.
What surprised Razib Khan — and me — it that modern Republicans do not lean more toward free trade than Democrats, according to a recent Pew survey:
The Republican party has long had a tension between populists who oppose free flow of labor (immigration) and are suspicious of international capital, and the economic elites. If the populists turn against the free flow of goods & service then the problem will be compounded. As for the Democrats, it looks like the economic nationalists and anti-globalists are fading. I’m updating my stereotypes as of now.