AQAP, the Al Qaeda affiliate in the Yemen, is widely viewed as the most violent of the lot; so when its leader, Ibrahim al-Asiri, singles out US lone-wolf attacks for praise and calls for more of them, the US security forces are right to be concerned. The United States has been fighting a war against al Qaeda, which it views as an existential threat to American interests, since 2001.
AQAP, the Al Qaeda affiliate in the Yemen, is widely viewed as the most violent of the lot; so when its leader, Ibrahim al-Asiri, singles out US lone-wolf attacks for praise and calls for more of them, the US security forces are right to be concerned. Al-Asiri is believed to be developing a 'new generation' of wearable explosive devices (shoes, underwear etc.).