So, what does his record say? Is Obama the most liberal president in recent history or, as he contends, something well short of an ideological warrior?
Let's start with National Journal's vote ratings. There are three years -- 2005, 2006 and 2007 -- that can be analyzed. (Obama didn't vote enough on NJ's key votes in 2008 to register a score.)
In 2005, he scored 82.5, meaning that his voting record on a select number of economic, foreign policy and social issue votes was more liberal than roughly four in five Senators. That made him the 16th most liberal Senator in the chamber; Massachusetts Sen. Ted Kennedy -- 96.7 score -- was the most liberal. In 2006, Obama's composite liberal score moved up to 86, good for 10th highest in the chamber. In 2007, as he spent more and more time running for president, he scored 95.5 -- making him the single most liberal-voting Senator that year. Republicans made much hay out of that fact although it is worth noting that Obama missed one-third of the 99 votes NJ used to make its calculations.
Obama, asked about his voting record, took issue with the way National Journal calculated the rankings. "It is true that when you look at some of the votes that I've taken in the Senate that I'm on the Democratic side of these votes, but part of the reason is because the way these issues are designed are to polarize," he told "Fox News Sunday" host Chris Wallace in April 2008. "They're intentionally designed to polarize."
Obama is not alone in critiquing the NJ system of rankings. Many political scientists view them as far too arbitrary and, as such, not fully reflective of a politician's ideological positioning versus his or her colleagues. (Here's an explanation of how National Journal calculates its vote ratings.)
That brings us to the DW-Nominate scores, a complex rating system developed by a half-dozen political scientists that ranks politicians from -1 (very liberal) to 1 (very conservative).
As a baseline to judge Obama, let's use the average DW-Nominate score for Senate Democrats in the 113th Congress: -.341. In the 109th Congress, which lasted from 2005-2007, Obama's DW-Nominate score was -.411 -- slightly to the left of the current average. But, he was hardly the most liberal Senator; Iowa Sen. Tom Harkin had a -.502 score while Kennedy had a -.494. In the 110th Congress (2007-2009), Obama's DW-Nominate score moved slightly more liberal to -.419. But, he was still not the most liberal voting Senator.
What about Obama's record since he was elected President? (Remember that Obama has now been president longer than he served in the Senate.) Making calculations about Obama as president is tough since, unlike his time in the Senate, he doesn't have any sort of voting record. But, the political scientists behind DW-Nominate have constructed rankings for presidents as well -- based on public positions they have taken on Senate and House roll call votes.
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.
Here's their chart detailing the DW-Nominate scores for our recent presidents:
Looking back then at his near-decade in federal office, the numbers would suggest that Obama is slightly more liberal than his former Senate colleagues but less liberal than many of his Democratic predecessors in the White House. Of course, any single numeric measurement of a politician's ideology can be questioned since data are context free and takes a politician out of the times in which they are governing. Still, the data are the data. And it suggests that while President Obama is quite clearly on the liberal end of the spectrum, he is far from its most extreme point.