Taking military action in Syria might need Congress' approval, he said, and destroying ISIS will take time and effort.
This blog will get you up to speed on how the terror group known as the Islamic State in Syria and Iraq became so powerful, the investigations into the murders of journalists James Foley and Steven Sotloff and what might be next.
ISIS' brutality is their calling card, the way that they energize their base, CNN's Paul Cruickshank, a longtime terrorism expert and CNN analyst has said. Tuesday's video showing a masked man standing behind journalist Stephen Sotloff would likely rev up ISIS' followers, Cruickshank said.
The man, speaking in an apparent British accent, raised a knife and threatened President Obama: "Just as your missiles continue to strike our people, our knife will continue to strike the necks of your people."