Barack Obama ranked as the most liberal senator of 2007, according to newly released National Journal ratings.

National Journal has tabulated the rankings of U.S. senators and representatives based on their votes for the last 27 years, and found that in 2007 both Obama and his rival for the Democratic presidential nomination Hillary Clinton shifted to the left in the run-up to the primaries.

Obama went from being the 10th-most-liberal senator in 2006 to the front of the line, while Clinton went from being the 32nd-most-liberal senator to the 16th-most-liberal last year.

Despite the bitterness pervading the campaign between Clinton and Obama, National Journal pointed out the two have very similar voting records. The year-in-review showed the two differed on just 10 of the 267 measure they both voted on.

The article said the two candidates were like "fraternal policy twins," demonstrating only slight differences.

National Journal wrote that the two senators supported most measures to withdraw troops from Iraq and comprehensive immigration reform, and that they voted similarly when it came to health care, education, energy and other issues.

In response, Obama spokesman Bill Burton dismissed the use of labels like conservative and liberal.

"Only in Washington can you get falsely attacked for being like Reagan one week and labeled the most liberal the next," he said. "The tendency of Washington to apply a misleading label to every person and idea is just one of the many things we need to change about how things operate inside the Beltway.

Click here to read more about the National Journal rankings.