“It was very clear to people how bad these guys are,” Michael Leiter, a former top counterterrorism official in both the Bush and Obama administrations, said in an interview. “I don’t know if this was a tactical error or an intelligence error.”

Any question about the group’s capabilities or intentions should have been answered when the militants took Fallujah in January, Leiter said.

“I think our intelligence has failed us miserably, from not being aware of the threat that we’ve faced and how this could unfold as quickly as it has. This has been planned for quite some time,” Sen. Joe Manchin, a Democrat from West Virginia, said on NBC’s Meet The Press Sunday. “My first thing to recommend to the president is get your intelligence group back on track, making sure that we have the intel that we need for whatever options we have, that are going to be accurate.”