Afghan President Hamid Karzai arrived in Tehran Sunday at the head of a large delegation and was received by President Hassan Rouhani. The trip was an act of defiance against Obama administration in the crisis over his refusal to sign an agreement covering a US military presence in the country after the bulk of the force leaves next year. Saturday, when US Defense Secretary Chuck Hagel arrived in Kabul, Karzai made no attempt to see him. A complete US troop withdrawal from Afghanistan would leave a security void in the country and invite the bloody chaos to which Iraq has succumbed.