The United States is not ready to credit the Islamic State terror group with carrying out Sunday's attack on a convention center outside Dallas, Texas.
White House spokesman Josh Earnest told reporters Tuesday that it was too early to say whether the gunmen had any ties to the terror group, but he credited law enforcement with foiling "what appears to be an attempted terrorist attack."
"This is still under investigation by the FBI and other members of the intelligence community to determine any ties or affiliations that these two individuals may have had with ISIL or other terrorist organizations around the world," Earnest said, using an acronym often applied to the Islamic State group.
Islamic State claimed credit for the attack Tuesday on its radio station, saying "two of the soldiers of the caliphate" carried out the attack in the Texas town of Garland, where a contest for cartoons depicting Islam's Prophet Muhammad was taking place.
"We tell America that what is coming will be even bigger and more bitter," IS said in its statement, the first time it has claimed responsibility for an attack on U.S. soil.
Police in Texas identified the assailants in the attack as Elton Simpson, 31, and Nadir Soofi, 34, who shared an apartment in Phoenix. The pair opened fire on the conference center, wounding a security guard before they were shot and killed by a Garland police officer.
Court documents show that Simpson had been under surveillance since 2006 and was convicted in 2010 of lying to FBI agents about his desire to join violent jihad in Somalia.
For now, Islamic State's claim of responsibility is being met with a degree of skepticism.
"The Islamic State is an interesting terrorist group in the sense that it's not fussy over claiming credit for attacks or accepting members into the group," said Max Abrahms, a terrorism expert at Northeastern University in Boston and a member of the Council on Foreign Relations. "This is why Islamic State appears to be everywhere, because it claims credit for any possible attack that could be connected to the group."
Abrahms said the rush to claim responsibility pointed to the group's overall weakness and lack of support in the U.S.
"The perpetrators were well-armed, but luckily they were very incompetent, and I think that just shows how desperate the group is to try to claim even foiled attacks as successes," he said.
FBI agents and police searched the Phoenix apartment Simpson and Soofi shared, cordoning off the complex and evacuating residents for several hours. Still, the White House said Tuesday that the nation's intelligence agencies were still trying to determine whether the two men got any instructions from Islamic State or another group, or whether they simply were inspired by propaganda on social media.
"We're very vigilant about the efforts that are under way by ISIL and other extremist organizations to try to radicalize some individuals in the United States," Earnest said. "We're working closely with community leaders, law enforcement officials, of course, to try to counter that threat."
In some ways, whether Simpson and Soofi had orders from a terror organization like Islamic State or were acting as so-called lone wolves may not matter, according to former U.S. Ambassador Mark Wallace, now chief executive officer at the Counter Extremism Project, a nonpartisan policy group.
"Social media has changed the relationship between extremist groups and those that are inspired by extremist groups. They have much broader reach," he said. "That's the new normal, and it's a normal that we can't live with."
Other experts also see another worrying trend: radicalized individuals who wait years before they take action, almost as if they were part of a so-called sleeper cell.
"Many of the fears that we had right after 9/11 are starting to come true," said Brian Fishman, a counterterrorism research fellow at the New America Foundation, a public policy group based in Washington. "In the last year, really, we've seen a number of attacks by individuals that have gotten training or had some sort of connection abroad and then came home and sat dormant for some time."
Perhaps the most notable parallel is the January attack on the French satirical magazine Charlie Hebdo, carried out by brothers Said and Cherif Kouachi, which left 12 people dead.
In that case, at least one of the gunmen had been under surveillance by French authorities, suspected of training in Yemen before returning to France, where he kept a low profile until the attack. In the Texas case, one of the two men had been under surveillance since 2006.
Fishman said long periods of inactivity are a challenge.
"The FBI may get some indication that an individual's a threat, but they have to make a very difficult resourcing decision about whether or not individuals are actually a threat and which individuals are the largest threat," he said. "They are never going to be 100 percent."