The fact that they're onboard for strikes -- McCain went so far to says that a failure of Congress to back the president would be "catastrophic" -- tends to undermine the second thing they're after here, which is to try to use the President's need for their support to extract greater commitments from Obama to aid the Syrian rebels. In their words, they'll back Obama's effort to "degrade" Assad's chemical weapon capabilities if it's accompanied by an "upgrade" to rebel capabilities. Some of those upgrades are already underway; McCain and Graham want more. But they're not seriously threatening to withhold support.
The White House may toss them a bone with some additional symbolic aid to the rebels, but you can put McCain and Graham down as firmly in support of even limited intervention. The rest is posturing and preening.