In a rare Oval Office address, Obama sought to calm a U.S. public increasingly jittery about the fight against Islamist militancy that once appeared to be waged overseas. His remarks failed to quiet Republican critics who have long accused him of underestimating the militants' strength and staying power.
Speaking in a measured tone, Obama used his 14-minute nationally televised appearance to draw a careful line about what he would and would not do. He pledged, for example, to "hunt down terrorist plotters" anywhere they are. But he insisted: "We should not be drawn once more into a long and costly ground war in Iraq or Syria."
Obama spoke just four days after U.S.-born Syed Rizwan Farook and his wife opened fire on a holiday party for civil servants in San Bernardino, California, killing 14 people. The pair were killed hours later in a shootout with police.
Obama condemned the attack as "an act of terrorism designed to kill innocent people." But he also said San Bernardino showed that "the terrorist threat has evolved into a new phase" as Islamic State used the Internet to "poison the minds" of potential assailants.