More from political scientist Keith Poole at the Voteview blog:
We find that President Obama is the most ideologically moderate Democratic president in the post-war period, with a first dimension DW-NOMINATE Common Space score of -0.329. President Lyndon Johnson, the second-most moderate Democratic president in this period, has a score of -0.345. President Obama’s ideological position is estimated from his “votes” (statements of support or opposition) on 282 congressional roll call votes. This amount is somewhat low; for example, President George W. Bush “voted” 453 times during his last term in office. However, it is adequate to recover his latent ideological score.
Among members of the 112th Congress, President Obama is ideologically closest to Rep. Jim Moran (D-VA), whose score is -0.328. President Obama is also proximate to Senators Bob Casey (D-PA, -0.332), Kent Conrad (D-ND, -0.326), the recently deceased Daniel Inouye (D-HI, -0.331), and Jeanne Shaheen (D-NH, -0.317). Among Democratic Congressional leaders, President Obama is to the left of Senate Majority Leader Sen. Harry Reid (D-NV, -0.304), and to the right of House Minority Leader Rep. Steny Hoyer (D-MD, -0.395), Senate Majority Whip Sen. Dick Durbin (D-IL, -0.401), and House Majority Leader Rep. Nancy Pelosi (D-CA, -0.530). Interestingly, President Obama has a nearly identical score to former Senate Democratic Leader Sen. Tim Daschle (D-SD, -0.328), whom President Obama had initially nominated for Secretary of Health and Human Services after controversy over unpaid taxes.
Using their metric,* which looks at issue where a given president has taken a clear stand (and which therefore excludes rhetorical or symbolic pronouncements), we get the following going back to Truman:

It is worth noting that Obama’s predecessor was the most conservative in the post-war period, which is relevant to any short-term comparisons of ideological comparison, given the short-term perceptions that shape our politics.
The write-up goes on to note:
Our results may seem surprising to those who consider President Obama among the most — even the most — liberal president of the post-war era. We would respond with a couple of observations. First, President Obama has tacked to the right on many national security and foreign policy issues. For example, President Obama — who once opposed FISA (The Foreign Intelligence Surveillance Act ) — recently supported and signed legislation a five-year extension of the program. Drone strikes — certainly not a source of liberal enthusiasm, even if vocal opposition from the left has been absent under President Obama — have been central to foreign policy during the Obama administration. Furthermore, while foreign policy issues come up relatively infrequently in congressional roll call voting, they constitute a greater proportion of the votes on which the president (i.e., the commander in chief) announces a position.
All of this is simply more evidence to suggest that the notion that Obama is especially liberal (let alone a socialist of some stripe) is an indefensible position to take from an empirical point of view.
Of course, as I noted in a related post yesterday, 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. At least this is what the date suggests.
*They use the CQ Presidential Support Scores









