The National Journal scored Obama the Most Liberal Senator in 2007:
Sen. Barack Obama, D-Ill., was the most liberal senator in 2007, according to National Journal‘s 27th annual vote ratings. The insurgent presidential candidate shifted further to the left last year in the run-up to the primaries, after ranking as the 16th- and 10th-most-liberal during his first two years in the Senate.Sen. Hillary Rodham Clinton, D-N.Y., the other front-runner in the Democratic presidential race, also shifted to the left last year. She ranked as the 16th-most-liberal senator in the 2007 ratings, a computer-assisted analysis that used 99 key Senate votes, selected by NJ reporters and editors, to place every senator on a liberal-to-conservative scale in each of three issue categories. In 2006, Clinton was the 32nd-most-liberal senator.
How about some conservatives?
Sen. John McCain, R-Ariz., the only other senator whose presidential candidacy survived the initial round of primaries and caucuses this year, did not vote frequently enough in 2007 to draw a composite score. He missed more than half of the votes in both the economic and foreign-policy categories. On social issues, which include immigration, McCain received a conservative score of 59.Rep. Ron Paul, R-Texas, the lone House member still in the presidential race, had a composite conservative score of 60.2, making him the 178th-most-conservative lawmaker in that chamber in 2007. His libertarian views placed him close to the center of the House in both the social issues and foreign-policy categories. He registered more conservative on economic issues.