Top officials have long been warning about the threat posed by ISIS . The group has claimed responsibility for a number of attacks in recent years and is believed to be behind several plots against Western targets. It was also hard to predict Iraq 's defense capabilities , the White House says .
Top officials have long been warning about the threat posed by ISIS . President Obama said the U.S. `` underestimated '' the group 's rise in Syria . It was also hard to predict Iraq 's defense capabilities , the White House says .