National security expert urges DHS to raise terror threat level, warns of sleeper cell risks in US

A national security expert is urging the Department of Homeland Security (DHS) to raise the national terror threat level following a shooting that investigators say may be linked to terrorism, warning that sleeper cell activity within the United States poses an escalating danger.

"We are facing a wide variety of threats here, and the problem is, they're all located within our own borders right now," former DHS advisor Charles Marino said Monday...