The suspect in the deadly shooting at a military recruiting center in Arkansas is the latest in a series of Muslim converts accused of planning or launching violent attacks in the U.S., part of what security experts call an alarming domestic trend. The attack came less than two weeks after a foiled bomb plot on two synagogues in Riverdale, N.Y., allegedly led by four men who converted to Islam in prison or shortly after their incarceration. Abdulhakim Mujahid Muhammad, the 23-year-old accused of killing a U.S. soldier and injuring another in the attack Monday in Little Rock, was born in...