"We could use our precision strike capabilities to target Assad's aircraft and SCUD missile launchers on the ground without our pilots having to fly into the teeth of Syria's air defenses," McCain said. "Similar weapons could be used to selectively destroy artillery pieces and make Assad's forces think twice about remaining at their posts. We could also use Patriot missile batteries outside of Syria to help protect safe zones inside of Syria from Assad's aerial bombing and missile attacks. 

"Would any of these options immediately end the conflict? Probably not. But they could save innocent lives in Syria."

Levin, the chairman of the Senate Armed Services Committee, said it was “essential” that the U.S. “step up the military pressure on the Assad regime.”

He did not specify what actions should be taken, but said military pressure would send Assad the message that “he will go one way or another.”

Menendez, the chairman of the House Foreign Relations Committee, introduced legislation earlier this week that advocates arming the Syrian rebels in order to help them topple the Assad regime.

No senators have called for the U.S. to put boots on the ground in Syria, but Graham on Thursday said the U.S. should arm and train the “right rebels.”

“I would suggest that a bipartisan consensus is forming in the Senate that it is now time to do more, not less in Syria,” Graham said. “We should be arming the right rebels.”

McCain and Graham warned that in the absence of the U.S., radical jihadists are helping the Syrian opposition, which isn’t in the best interests of the U.S. in the long run.

Pressure on the administration to take firmer action with Syria has mounted in recent weeks amid reports that Assad’s regime may have used chemical weapons against its opponents.

Yet those reports have been unconfirmed so far, and Obama and the White House have repeatedly said they will look for more information before stating definitively that chemical weapons were used by the regime.

Obama has previously called the use of chemical weapons a red line, but the White House has said Obama has not specified what actions could be triggered by its crossing.

McCain said on the floor Thursday that it is clear that Assad has used chemical weapons against opposition within his country.

“There is mounting evidence that chemical weapons have been used by the Assad regime,” McCain said. “Obama’s redline has been crossed … yet he called for [United Nations] investigators that still haven’t even reached the ground and they may never. … It will not be long before Assad sees this delay as an invitation to use chemical weapons again. … It essentially gave Assad a green light to use every weapon in his arsenal,” he said.

The bipartisan group of senators said the U.S. should militarily help rebels in the region in order to get Assad to negotiate or step down.

“The longer we wait, the worse the situation gets, and the tougher it will get for us to address the situation, which we will eventually have to do,” McCain said. He added that "moral dimensions” must be “restored to our deliberations,” or Obama would have “presided over the mutilation of consciences from discourse.”

This article was updated at 2:30 p.m.