KABUL, Afghanistan — Tens of thousands of people in Afghanistan waited nervously on Saturday to see whether the United States would deliver on President Joe Biden’s new pledge to evacuate all Americans and all Afghans who aided the war effort. Meanwhile, the Taliban leader arrived in Kabul for talks with the group’s leadership on forming a new government. Time is running out ahead of Biden’s Aug. 31 deadline to withdraw most remaining U.S. troops, and the president on Friday night did not commit to extending it. He faces growing criticism as videos depict pandemonium and occasional violence outside the airport,...