President Joe Biden, on the 20th anniversary of the Sept. 11 terror attacks, defended his decision to withdraw U.S. troops from Afghanistan but acknowledged that the terrorist group al-Qaeda may attempt to reconstruct itself in the country following the Taliban takeover. The president, who marked the anniversary of the Sept. 11, 2001 attacks by visiting all three sites where the hijacked planes crashed, told reporters he believes the terrorist group could “come back.” “Could al Qaeda come back? Yeah,” Biden told reporters in Shanksville, Pennsylvania, where one plane went down after crew and passengers fought with hijackers. “But guess what? It’s already back [in] other places. What’s the strategy? Every place where al Qaeda is, we’re going to invade and have troops stay in? Come on.” The Biden administration’s evacuation efforts came to a halt on Aug. 30, with the final U.S. flight of evacuees leaving Kabul’s international airport hours …