Huw Richards reports from the American Political Studies Association's conference in Chicago.
Conventional wisdom about the history of party politics in the United States is largely based on the concept of "realignment" and periodic changes in the relationship between the two main parties - in 1860, 1896 and 1922.
But John Gerring of Boston University has analysed campaign rhetoric and come up with a different model based on ideological shifts. This reveals a single shift by the Republicans during the 1920s and two by the Democrats - "The Democrats are always more complex and messier" - in the 1890s and the late 1940s.
In contrast to analysts who have argued that party competition is essentially non-ideological, Professor Gerring says both parties have consistent ideological cores. He describes the first Democrat incarnation, running from the 1820s to the 1890s, as "Civic Republicanism". "It is concerned with values of liberty against tyranny, states' rights and white supremacism," he told the American Political Studies Association annual conference in Chicago.
In the 1890s, with William Jennings Bryan in the ascendant, there is a shift to populism. "Anti-statism disappears and the predominant theme becomes the people versus the interests, accompanied with a considerable level of 'class resentment' and derogatory statements about the rich and big business. This lasts through to the 1940s. Harry Truman was the last populist president. This was replaced from the 1950s on by a rights-based universalism emphasising the importance of an inclusive society."
The consequence of this analysis is that the New Deal policies of Franklin D. Roosevelt are seen as representing continuity with Democratic ideology stretching back to the days of Bryan. He sees the single shift in Republican outlook coming just before the New Deal rather than in response to it.
"The earlier Republican ap-proach was nationalist and concerned with maintaining order against possible anarchy. It feared social breakdown if institutions of the social order were threatened and was protectionist, concerned with moral reform and statist," he said.
"In the 1920s this gives way to neo-liberalism, concerned with protecting the individual from the state. Up to the 1920s the majority of Republican references to the state are approving, after then always negative."
He argued that these shifts are a consequence of action by party elites rather than the mass of voters. "Mass attitudes have much more to do with minor shifts in the way parties position themselves than in the major ideological shifts. They are generally forces of constraint rather than dynamism."
Professor Gerring accepted the point made by one member of his audience, that the detailed knowledge of public opinion possessed by the modern politician made major ideological shifts more difficult.
He suggested that shifts in ideology were a response by party leaders to changing external circumstances. "By the 1920s tariffs - the defining issue for earlier Republicans - had lost importance. Labour had been redefined as Organised Labour. A sizeable middle-class and a consumer future had appeared. With 'red scares' the fear of communism had replaced that of anarchy. The growth of federal government during the first world war had alarmed many small businessmen. Attempts at moral reform like temperance were clearly failing".