SANTA ANA, Calif. — A federal judge on Monday sentenced a California man to 15 years in prison for trying to join the Islamic State group in Syria, calling his conduct a serious threat to the U.S. and saying it was influenced by his abusive childhood and history of mental problems. Orange County native Adam Dandach, 22, was also ordered to undergo supervised release for the rest of his life after he pleaded guilty last year to trying to provide material support to a terror group and lying on his passport application. The case against Dandach is one in a series involving young men in states ranging from California to Georgia who have been charged with trying to assist Islamic State and other groups. The U.S.