WASHINGTON — The suicide bomber waited until the last possible moment, U.S. officials said.
A crowd straining to get into Hamid Karzai International Airport had converged on Abbey Gate, a main entryway manned by Marines and other service members. The troops knew that they could be targeted in an attack; just the day before, the State Department had warned of a “credible” threat at three gates at the airport, where more than 5,000 American troops had helped to evacuate more than 100,000 people in less than two weeks. Abbey Gate was on the list.
Airport security had closed two of the gates, but decided to leave Abbey Gate open, U.S. officials said.
They also said that, earlier in the day, Taliban commanders and fighters manning checkpoints along the airport route twice pushed back surging crowds, but they came back again.
That third time, someone else came with them.
At 5:48 p.m., the bomber, wearing a 25-pound explosive vest under clothing, walked up…