The two senators, both likely contenders for the 2016 presidential race were voting against an amendment offered up by Vermont independent Bernie Sanders. Democrats have repeatedly offered up such amendments—which in the current Senate have no chance of passing—in order to highlight Republicans' positions on climate change, betting it will repel swing voters.
Indeed, nearly all of the Senate's 54 Republicans voted against the amendment. The five exceptions: Kelly Ayotte, Susan Collins, Lindsey Graham, Mark Kirk, and Rob Portman—all of whom voted for the amendment. Ayotte, Kirk, and Portman all face contested races in purple states in 2016, while Graham is eyeing a White House bid and has been one of few Senate Republicans urging action to address climate change.
The vast majority of scientists say that global warming is real and caused by human activity, but public opinion is divided and endorsing climate science can land Republicans in hot water with their base.
Earlier this week, presidential candidate Ted Cruz grabbed headlines when he compared climate activists to "flat-Earthers." Cruz also said that satellite data shows that Earth has not experienced any significant warming in the past 17 years. Cruz was absent from Wednesday's vote. In previous statements, Rubio has expressed doubt over human contributions to climate change. Paul has said he believes human activity is partly responsible for climate change, but he also voted against an amendment saying the human contribution is significant.
Action on carbon emissions is an unpopular stance in states that produce large amounts of fossil fuels. Senators Joe Manchin of West Virginia (among the nation's largest coal producers) and Heidi Heitkamp of North Dakota (the heart of the oil-shale boom) were the only two Democrats to vote against the amendment.
The amendment ultimately failed to get the 60 votes needed to clear a filibuster. 49 Senators voted for the amendment while 50 voted against it.
CORRECTION: An earlier version stated in both the headline and the article that Ted Cruz voted against the amendment as well. Cruz was absent from the vote.