Mark Kirk is the most liberal Republican senator. He voted to repeal the Defense of Marriage Act, and endorsed same-sex marriage. He was one of four Republicans to vote to break a filibuster on the background check bill, and is the only member of his party to favor President Obama’s proposed assault weapons ban.
The reason? No Republican represents a more liberal state than Kirk. As you can see from this chart below, Illinois voted for Obama in greater proportion than any other state with a Republican senator. The only senator even close is Susan Collins of Maine, whose voting record is similar to Kirk’s. Collins voted to repeal DOMA and to break the background check filibuster.
Mark Kirk, Illinois 57.3 percent
Susan Collins, Maine, 56.3 percent
Ron Johnson, Wisconsin, 52.8 percent
Dean Heller, Nevada, 52.3 percent
Kelly Ayotte, New Hampshire, 52.2 percent
Chuck Grassley, Iowa, 52.1 percent
Pat Toomey, Pennsylvania, 52 percent
Rob Portman, Ohio, 50.1 percent
Marco Rubio, Florida, 50 percent
And here’s a list of Democrats representing states that voted for Romney. All four Democrats who voted to sustain the filibuster on the background check bill are in this list -- Max Baucus (who announced he's retiring), Mark Pryor, Mark Begich and Heidi Heitkamp. So are the three Democrats who oppose gay marriage -- Mary Landrieu, David Pryor and Joe Manchin.
Jay Rockefeller, West Virginia, 62.3 percent
Joe Manchin, West Virginia, 62.3 percent
David Pryor, Arkansas 60.7 percent
Kent Conrad, North Dakota, 58.7 percent
Heidi Heitkamp, North Dakota, 58.7 percent
Tim Johnson, South Dakota, 57.9 percent
Mary Landrieu, Louisiana, 57.8 percent
Mark Begich, Alaska, 55.3 percent
Max Baucus, Montana, 55.3 percent
Jon Tester, Montana, 55.3 percent
Joe Donnelly, Indiana, 54.3 percent
Claire McCaskill, Missouri, 53.7 percent