The United Nations is back in Syria. A day after one team of chemical weapons inspectors left Damascus, another has arrived. The convoy of about 20 U.N. vehicles crossed into Syria from Lebanon. This group of experts is charged with starting the process of verifying and eliminating Syria's chemical weapons. The U.N. mission comes after an August 21 chemical weapons attack in Damascus. That attack prompted U.S. threats of air strikes against the Syrian government.