To listen to both Hamas and ISIS, the two Islamist terror groups are enemies. As Foreign Policy noted back in May, Hamas views the Islamic State as a threat to its despotic hold on power in Gaza and destroyed a mosque affiliated with its followers. ISIS returns the sentiment, condemning Hamas for its brutal rule and vowing as recently as this weekthat it will topple them. What then should we make of the news coming out of Israel this week that Hamas provided vital help to ISIS’s deadly terror attack on Egyptian security forces in the Sinai. No doubt some of Hamas’s apologists will dismiss the claim as an attempt by Israel to discredit an enemy in the eyes of the West. But given the scale of the Sinai attack it is hard to believe that ISIS would have been able to pull it off without serious assistance and the only possible source of that help would have to be Hamas-ruled Gaza. If true, this should not only heighten concerns about the spread of ISIS throughout the Middle East but also call into question some of the assumptions that many in the foreign policy establishment have held about Hamas being a stabilizing rather than a purely destructive force in the region.