PBS | 9:00 pm

"America After 9/11" examines how the 2001 terror attacks on the United States carried out by 19 hijackers changed the course of history, scrambling the global geopolitical order and persuading American political leaders to compromise long-held principles out of fear of another attack. The U.S. response to that horrifying day not only transformed the Middle East, but America itself, and in very fundamental respects. As the 20th anniversary of those attacks approaches, this special episode looks at how 9/11 affected actions by four U.S. presidents.