From the article:
We find that President Obama is the most ideologically moderate Democratic president in the post-war period…
and
one of the reasons that many of the president’s partisan opponents make the claims that they do is not because Obama is more left-leaning than recent Democrats, but it is because Republicans have become more right-leaning. In other words, the relative vantage point between the parties at the moment is due not to a leftward lurch by the Democrats, but by a rightward move by the the Republicans.
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