The US has struggled to confront the rise of domestic terrorism threats, drawing concern from lawmakers and former officials that there is a lack of a cohesive strategy to deal with the problem and the limited resources available skew towards international efforts.

The FBI has seen a significant rise in the number of white supremacist domestic terrorism cases in recent months, a senior bureau counterterrorism official told CNN recently. Congress and the executive branch, critics say, have been slow to react.

A US Department of Homeland Security-sponsored study this year found that there are "major gaps in national terrorism prevention efforts," stemming from limited investment and a lack of focus. Federal initiatives have also been stymied by a "sustained opposition" to some if its terrorism prevention efforts.

Read more: CNN