National Journal is out with the 2010 edition of its famous annual rankings of where members of Congress sit on the ideological spectrum – and Sheldon Whitehouse was the most liberal U.S. senator for the second year in a row.

Whitehouse took the title of “most liberal” in a nine-way tie with senators from Ohio (Brown), Maryland (Cardin and Mikulski), Vermont (Leahy and Sanders), Michigan (Levin and Stabenow) and Nevada (Reid), according to the Beltway magazine. They voted for liberal policies 83% of the time.

Whitehouse’s Rhode Island colleague Jack Reed was right behind him, though, in a three-way tie for the ranking of 10th most-liberal senator along with New York’s two members, Kirsten Gillibrand and Chuck Schumer. Reed voted for liberal policies 81% of the time.

In the House of Representatives, now-retired Patrick Kennedy and Jim Langevin were further from the ideological extremes and also further apart from each other than the senators.

National Journal ranked Kennedy the 60th most-liberal congressman, voting that way 83% of the time, and Langevin as 120th most-liberal, voting that way 73% of the time.

Massachusetts Rep. Jim McGovern, who represents Bristol County, was in a three-way tie for eighth most-liberal congressman, according to National Journal. He took the liberal position in votes 95% of the time.

National Journal’s Ron Brownstein said the rankings showed Congress reaching “a new peak of polarization.” Here’s how he described the magazine’s findings overall:

The results document another leap forward in the fusion of ideology and partisanship that has remade Congress over the past three decades, the period tracked by NJ’s vote ratings. For most of American history, the two parties operated as ramshackle coalitions that harbored diverse and even antithetical views. … But since the early 1980s, they have vastly diminished as the differences within each party have narrowed and the distance between them has widened.

Over that period, “it’s just a straight, linear increase” in congressional polarization, says Gary Jacobson, a University of California (San Diego) political scientist who specializes in Congress. “There’s a little bit of bumping around in the numbers here and there, but the basic movement is toward the parties moving further and further apart. The 1970s are a high point of all the cross-party [coalitions]. The last three decades are ones of pulling apart.”

The magazine has been putting together the rankings since 1981. To do so, its researchers looked through all of last year’s roll-call votes in Congress – 664 in the House and 299 in the Senate – and determined which ones showed a clear ideological distinction. Just under 100 votes were used to do the calculations. More about the methodology is available here.