Sen. Mark Kirk, R-Ill., on Tuesday became the second Republican senator to declare his support for same-sex marriage.
“Life comes down to who you love and who loves you back,” he wrote on Twitter.
Kirk is the third senator in just three days to change his mind to support same-sex marriage, joining Democrats Tom Carper of Delaware and Bob Casey of Pennsylvania.
The new converts bring the total number of senators favoring gay marriage to 50 -- 48 of them Democrats or Democratic-leaning independents and two of them Republicans.
Meanwhile, 43 Republicans and seven Democrats oppose it.
As the numbers above demonstrate, there’s a clear gulf between the two parties on this issue. Indeed, according to a Dec. 2012 NBC News/Wall Street Journal poll, 69 percent of Democrats support same-sex marriage, compared with 63 percent of Republicans who oppose it.
But there’s also a striking pattern here: By and large, senators hailing from blue states that Barack Obama won in 2008 and 2012 support gay marriage, and those from red states oppose it.
Six of the seven Democratic senators who continue to oppose gay marriage serve states that went for Mitt Romney in 2012. Sen. Bill Nelson, D-Fla., is the only exception -- but Florida is a state Obama won last year by just 70,000 votes.
Similarly, the only two Republican senators to break from party orthodoxy and signal their support for gay marriage thus far -- Kirk and Rob Portman, R-Ohio -- represent states Obama has carried. Neither lawmaker is up for re-election until 2016.
On the flip side, seven Republicans who oppose gay marriage hail from states that Obama won in 2008 and 2012. But only one -- Susan Collins of Maine -- is up for re-election next year. Collins’ overall reputation as a moderate, plus the fact that Maine is one of just a handful of states nationwide where gay marriage is legal, makes her another Republican to watch on gay marriage.
Democratic senators who support gay marriage
Tammy Baldwin (D-Wis.)
Max Baucus (D-Mont.)
Mark Begich (D-Alaska)
Michael Bennet (D-Colo.)
Richard Blumenthal (D-Conn.)
Barbara Boxer (D-Calif.)
Sherrod Brown (D-Ohio)
Maria Cantwell (D-Wash.)
Benjamin Cardin (D-Md.)
Thomas Carper (D-Del.)
Robert Casey (D-Pa.)
Christopher Coons (D-Del.)
William Cowan (D-Mass.)
Richard Durbin (D-Ill.)
Dianne Feinstein (D-Calif.)
Al Franken (D-Minn.)
Kirsten Gillibrand (D-N.Y.)
Kay Hagan (D-N.C.)
Tom Harkin (D-Iowa)
Martin Heinrich (D-N.M.)
Mazie K. Hirono (D-Hawaii)
Tim Kaine (D-Va.)
Amy Klobuchar (D-Minn.)
Frank Lautenberg (D-N.J.)
Patrick Leahy (D-Vt.)
Carl Levin (D-Mich.)
Claire McCaskill (D-Miss.)
Robert Menedez (D-N.J.)
Jeff Merkley (D-Ore.)
Barbara Mikulski (D-Md.)
Christopher Murphy (D-Conn.)
Patty Murray (D-Wash.)
Jack Reed (D-R.I.)
Harry Reid (D-Nev.)
John Rockefeller (D-W.Va.)
Brian Schatz (D-Hawaii)
Charles Schumer (D-N.Y.)
Jeanne Shaheen (D-N.H.)
Debbie Stabenow (D-Mich.)
Jon Tester (D-Mont.)
Mark Udall (D-Colo.)
Tom Udall (D-N.M.)
Mark Warner (D-Va.)
Elizabeth Warren (D-Mass.)
Sheldon Whitehouse (D-R.I.)
Ron Wyden (D-Ore.)
Angus King (I-Maine)
Bernard Sanders (I-Vt.)
Republican senators who support gay marriage
Mark Kirk (R-Ill.)
Rob Portman (R-Ohio)
Republican senators who oppose gay marriage
Alexander Lamar (R-Tenn.)
Kelly Ayotte (R-N.H.)
John Barrasso (R-Wyo.)
Roy Blunt (R-Mo.)
John Boozman (R-Ark.)
Richard Burr (R-N.C.)
Saxby Chambliss (R-Ga.)
Daniel Coats (R-Ind.)
Tom Coburn (R-Okla.)
Thad Cochran (R-Miss.)
Bob Corker (R-Tenn.)
John Cornyn (R-Texas)
Mike Crapo (R-Idaho)
Ted Cruz (R-Texas)
Michael Enzi (R-Wyo.)
Deb Fischer (R-Neb.)
Jeff Flake (R-Ariz.)
Lindsey Graham (R-S.C.)
Chuck Grassley (R-Iowa)
Orrin Hatch (R-Utah)
Dean Heller (R-Nev.)
John Hoeven (R-N.D.)
James Inhofe (R-Okla.)
Johnny Isakson (R-Ga.)
Mike Johanns (R-Neb.)
Ron Johnson (R-Wisc.)
Mike Lee (R-Utah)
John McCain (R-Ariz.)
Mitch McConnell (R-Ky.)
Jerry Moran (R-Kan.)
Lisa Murkowski (R-Alaska)
Rand Paul (R-Ky.)
James Risch (R-Idaho)
Pat Roberts (R-Kan.)
Marco Rubio (R-Fla.)
Tim Scott (R-S.C.)
Jeff Sessions (R-Ala.)
Richard Shelby (R-Ala.)
John Thune (R-S.D.)
Patrick Toomey (R-Pa.)
David Vitter (R-La.)
Roger Wicker (R-Miss.)
Democratic senators who oppose gay marriage
Joe Manchin (D-W. Va.)
Heidi Heitkamp (D-ND)
Tim Johnson (D-SD)
Mary Landrieu (D-La.)
Mark Pryor (D-Ark.)
Joe Donnelly (D-Ind.)
Bill Nelson (D-Fla.)