The 10 Most-Liberal Senators: 2011 Vote Ratings -- PICTURES

1st (tie) Kirsten Gillibrand, D-N.Y. The issue that has brought Gillibrand the most attention by far is her call for repeal of the 17-year-old “don’t ask, don’t tell” policy barring openly gay military service members. She introduced legislation in July 2009. In National Journal's 2010 survey, she was tied with fellow Sen. Chuck Schumer of New York as the 10th most liberal member of the Senate. (Brendan Hoffman)

1st (tie) Jeff Merkley, D-Ore. In the Senate, Merkley has been a dependable liberal vote, particularly on economic and social issues. In 2011, he joined Maine Republican Olympia Snowe on a bill to give the president additional emergency authority to reduce gasoline prices and he joined Democrats Tom Udall of New Mexico and Amy Klobuchar of Minnesota on a proposal to bar filibustering of motions to proceed to legislation.

3rd (tie) Daniel Akaka, D-Hawaii Akaka, revered in Hawaii for his gentleness and modesty, was stung by a 2006 Time magazine article that called him “affectionate and earnest” but one of the five worst senators in terms of effectiveness. “I was taught not to be a show horse but a workhorse,” he told The Honolulu Advertiser then. “So, in a way, it’s been a part of me not to brag.” He will not seek reelection in 2012. (Liz Lynch)

3rd (tie) Dick Durbin, D-Ill. He is the Democratic whip and assistant majority leader, making him the second most powerful senator after Majority Leader Harry Reid. Durbin has compiled a largely liberal voting record, though he supported welfare reform in the 1990s and has always supported the death penalty. (Liz Lynch)

5th (tie) Barbara Boxer, D-Calif. Boxer’s voting record is among the most liberal in the Senate, and she has long been one of the chamber’s most outspoken members. During the Clinton years, Boxer was frustrated when Republicans held up nominations to the 9th U.S. Circuit Court of Appeals, long the most liberal in the country. During the Bush years, she held up nominations of judges she considered too conservative. In 2005, Boxer said she would “use all the parliamentary tools I’ve been given as a U.S. senator” to delay a vote on the confirmation of John Roberts to the Supreme Court, and she voted against both Roberts and Samuel Alito. (Liz Lynch)

5th (tie) Sherrod Brown, D-Ohio Brown was a proponent of including a government-run insurance option in the Democrats’ health care overhaul. Later in the year, he opposed Obama’s deal to allow the Bush-era tax cuts to continue. (AP Photo/Harry Hamburg)

5th (tie) Tom Harkin, D-Iowa Harkin, a Democrat first elected to the House in 1974 and the Senate in 1984, is an accomplished veteran of Capitol Hill who brings the attitude of the aggrieved outsider to his work. (Richard A. Bloom)

5th (tie) Barbara Mikulski, D-Md. On domestic policy, Mikulski is a strong advocate of abortion rights and a solid liberal, although she sometimes votes for Republican initiatives, such as the bipartisan Welfare Reform Act of 1996. (Chet Susslin)

5th (tie) Tom Udall, D-N.M. He belongs to a political clan well known in the West and nationally that is sometimes called the “Kennedys of the West.” Udall added the Foreign Relations Committee to his workload in 2011, expressing a desire to help ratify the Law of the Sea Treaty defining the international usage of oceans. The treaty has drawn fierce opposition from conservatives concerned about its infringement on U.S. sovereignty. (AP Photo/Susan Montoya Bryan)

10th Ben Cardin, D-Md. A rock-solid Democrat, Cardin was tied for most-liberal senator in National Journal’s 2010 vote rankings. With a seat on the influential Finance Committee, Cardin was at the center of the big legislative battles shaping up in the 112th Congress (2011-12). He introduced a bill with Chairman Max Baucus in January 2011 to repeal the “1099” provision to the health care law, which called for businesses to submit forms to the Internal Revenue Service for all purchases above $600, a requirement that many agree was overly burdensome for small businesses. (AP Photo/J. Scott Applewhite)