The mystery for me is why did all these senators oppose the idea of same sex marriage. Apparently its religious beliefs. Evangelical Christians are a significant part of the Republican Party.
The measure advanced in a 62-37 vote, with 12 Republicans voting in favor, allowing it to clear the required 60-vote hurdle to prevent a filibuster.
39 Republicans joined all Democrats in the House of Representatives to pass the law. Notable was Rep. Vicky Hartzler of Missouri who was the face of the movement in Missouri to ban gay marriage. She traveled across the state in 2004, urging Missourians to add an amendment to the state constitution defining marriage as between a man and a woman. She reportedly cried on the floor of the House pleading with others to oppose this law.
The list of Republicans senators who voted against the Respect for Marriage Act are as follows:
- John Barrasso, WY
- Marsha Blackburn, TN
- John Boozman, AR
- Mike Braun, IN
- Bill Cassidy, LA
- John Cornyn, TX
- Tom Cotton, AR
- Kevin Cramer, ND
- Mike Crapo, ID
- Ted Cruz, TX
- Steve Daines, MT
- Deb Fischer, NE
- Lindsey Graham, SC
- Chuck Grassley, IA
- Bill Hagerty, TN
- Josh Hawley, MO
- John Hoeven, ND
- Cindy Hyde-Smith, MS
- Jim Inhofe, OK
- Ron Johnson, WI
- John Kennedy, LA
- James Lankford, OK
- Mike Lee, UT
- Roger Marshall, KS
- Mitch McConnell, KY
- Jerry Moran, KS
- Rand Paul, KY
- Jim Risch, ID
- Mike Rounds, SD
- Marco Rubio, FL
- Rick Scott, FL
- Tim Scott, SC
- Richard Shelby, AL
- John Thune, SD
- Patrick Toomey, PA
- Tommy Tuberville, AL
- Roger Wicker, MS
Coast Contact 
They also voted against protecting interracial marriage. Interesting to note that McConnell is married to a chinese woman and justice Thomas is married to a white woman.