Twenty-two senators -- twelve Democrats, nine Republicans and one Independent -- voted against the Title X measure included in the continuing resolution to fund the government until mid-December.
“There is no guarantee of success,” Rubio said of training and arming Syrian fighters. “But there is a guarantee of failure if we do not even try, and try we must.”
Rubio’s affirmative vote hawkishly distanced the Florida Republican from Sens. Ted Cruz of Texas and Rand Paul of Kentucky, who both opposed the measure.
Cruz said that the moderate rebels in the Free Syrian Army would use American weapons and training against the Assad regime over ISIS.
“Resolving the Syrian civil war is not our mission, nor the job of the military,” Cruz said on the floor Thursday.
Paul, who has worked to distance himself from the “isolationist” label, said weapons provided to moderate rebels would end up with ISIS, but insisted he was not opposed to intervention.
“There are valid reasons for being involved, and I think we are doing the right thing but just in the wrong way,” Paul said of voting on Title X as part of the continuing resolution.
These decisions could help distinguish Warren and Sanders from Clinton should they face off in 2016. While she did not weigh in on the Title X authorization specifically, Clinton urged President Obama to arm the Syrian rebels during her time as secretary of state.
Though he supports U.S. airstrikes, the Alaska Democrat said that Arab nations “need to step up to the plate” against ISIS. His Republican opponent, former state attorney general Dan Sullivan, supports arming the Syrian rebels.
Senators worried about the impact of their votes on potential presidential bids have some more fretting to do: they will have to vote on arming and training rebels once again when Title X expires in mid-December.
ABC News' Arlette Saenz and Jeff Zeleny contributed to this report.