"If extremism is a problem in presidential politics, it seems to be at least as much of a problem for Democrats as for Republicans," said study author Larry Bartels of Vanderbilt University in Nashville, Tennessee.
The findings, published in the journal The ANNALS of the American Academy of Political and Social Science, suggest that neither party's candidates are more than minimally responsive to the preferences of the swing voters whose views define the center of the political spectrum.
"My findings provide ample grounds for alarm for anyone who believes that presidential candidates should be responsive to the views of swing voters," Bartels said.
Bartels compared the positions of presidential candidates from 1980 to 2012 on a variety of political issues to the preferences of swing voters and of their own core supporters.
He used data from American National Election Studies surveys, utilising a "liberal-to-conservative" 100-point scale and adding viewpoints on government spending, government jobs, aid to African Americans, and defense spending.
Bartels concluded that the candidates' unresponsiveness to swing voters is not merely a reflection of the influence of core party members.
The parties' respective bases have indeed become more polarised in recent years, with the Republican base making the more substantial shift.
However, candidates' positions are frequently even more "extreme" than those of their core supporters.
"The idea that candidates' positions reflect strategic compromises between the preferences of core partisans and swing voters fares poorly here," Bartels wrote.
"Perhaps they reflect the influence of much smaller, more extreme subsets of 'intense policy demanders' or big donors, activist groups, and grassroots conservative or liberal organisations distinct from the larger cadres of core partisans," he noted.
