National security and civil rights analysts said the U.S. government's response to the Boston bombings will depend on details that emerge from the ongoing investigation, specifically whether the brothers accused of carrying out the attacks had direct connections to a foreign terrorist organization, were inspired by the ideology of radical Islam or had other motivations.
The two men, Dzhokhar Tsarnaev and Tamerlan Tsarnaev, were immigrants who had been in the United States for roughly a decade. They were part of a family with ties to Chechnya, a volatile region where Muslim separatists have been engaged in a bloody campaign against the Russian government for decades.
If there are connections to Islamist militant groups, including help planning and carrying out the attack, the Obama administration could expand intelligence-gathering efforts overseas, as well as widen surveillance and screening measures in the United States. But such measures would likely be controversial and far from foolproof.
If, however, the Tsarnaev brothers carried out the bombings with no foreign assistance, the administration's policy options may be more limited.
National security and legal experts note that the United States has endured violence committed with the kind of relatively small-size explosive devices used by the accused brothers for decades, attacks carried out by radical groups with ideologies that span the political spectrum.
Benjamin Wittes, a senior fellow at the Brookings Institution who tracks counterterrorism policy and law, said the administration would have to move carefully if it sought to expand surveillance in public spaces or increase monitoring of Muslim communities.
It's a "scenario in which you are almost powerless in a policy matter," Wittes said. "You obviously have to begin thinking about additional security at marathons and other events. But just as school shootings are really hard to prevent . . . I really don't think there's much more to do from a policy aspect."