The Democrat party began as a coalition of anti-federalists who had been opposed to the new Constitution because it gave the federal government too much power, and therefore they favored the next best thing: a strict construction of its text. Its original exemplar was, as noted, the Jeffersonian "yeoman farmer," who was succeeded in turn by the Jacksonian backwoodsman. These were the original Democrats, and they lived in, and sired the people who still live in, "fly-over country."
By contrast Alexander Hamilton, the great-grandfather of the Republican party, was an urban cosmopolitan. A rootless bastard born in the West Indies, his home was the big city which to him was not a symbol of decadence but of vitality. With accountant's ink for blood, he created Pat Buchanan's ultimate nightmare--the National Bank!!! (Ironic when one considers how Hamiltonian Buchanan is in his other views.)
Hamilton, and the Federalists, Whigs, and Original Republicans who succeeded him, believed in federal supremacy and loose construction of the Constitution (contrary to contemporary mythology, laissez faire was never the doctrine of American business, which has always been interventionist, but of Jeffersonian agrarianism). The "heartland" of Republicanism and its antecedents was the coasts--New England, California, and the Pacific Northwest. In the Election of 1896 it was the Coasts that voted for the conservative McKinley while the Bible-Belt Heartland was frothing at the mouth for the radical William Jennings Bryan.
The closest I can come to pinpointing the point at which all this changed was the New Deal, when Jefferson's Democrat party adopted Hamilton's interpretation of the Constitution (though one could say that the Bryanites had already done this) and Ivy League grads, formerly staunch Hamiltonians and McKinleyites, began to spy for the Soviet Union. And even here, the New Deal was king in the traditional Jacksonian areas. In fact, in the FDR landslide of 1936 the only states to go Republican were Maine and Vermont!
Nevertheless, the New Deal seems to have been the beginning of the reversal of ideologies and attitudes among the two parties. And as an unabashed and unashamed Hamiltonian, this fact gives me no joy whatsoever.
The book Blacklisted By History also spells this out. However, the book I am reading now - Liberal Facism - really lays it out. Theodore Roosevelt and Woodrow Wilson were both Progressives.
I am coming to the conclusion where I think that today's modern Republican Party - the policies and beliefs - actually originated in the 50's with William Buckley and his gang. It took a step forward with Barry Goldwater and then the next step was Ronald Reagan.
I think the next step may be Sarah Palin.