The ground war in Afghanistan has skidded to its predictable, spectacularly unsuccessful conclusion, but the War on Terror, launched twenty years ago this week, lives on. To what end?

One measure of a revolution’s legacy is what becomes normal in its wake. To explain the legacy of September 11 is thus partly to ask what is taken for granted in the post-9/11 world. How did the attacks alter the questions we ask—and the answers we give—about the challenges we face as a nation? What distribution of wealth and power now seems so normal that it largely escapes critical reflection? And in service of this new normal, what institutions and practices did we create and embed in U.S. life?

There are four key legacies of 9/11. First, it radically changed our understanding of war. Second, it launched the surveillance state and narrowed our conception of privacy. Third, it elevated border security to a matter of national survival. And, fourth, by creating the impression that the stakes were not merely consequential but existential, the attacks of September 11 normalized previously unimaginable cruelty.

As a civil rights lawyer, I have spent much of the past twenty years challenging various aspects of the post-9/11 state, a journey that so far has included three Supreme Court cases on behalf of detainees. I have seen these changes, and the damage they inflict, firsthand.

The most important legacy of 9/11 is the change it produced in our understanding of war. Though today it is hard to imagine, prior to 9/11, transnational terror was understood to be a crime, not an act of war. That framing collapsed before the sun set September 11. “This is obviously an act of war that has been committed on the United States,” said Senator John McCain on September 11. “Everybody said it all day,” Peter Jennings of ABC News correctly observed. It was, Jennings continued, “a declaration of war, an act of war against the United States. Any number of politicians and commentators, us included, who were reminded that the last time there was an attack like this on the United States was Pearl Harbor.”

President George W. Bush adopted this framing as well, beginning on September 12. After meeting with his national security team, he told reporters the attacks “were more than acts of terror. They were acts of war.” The next day, after a morning call with New York City mayor Rudolph Giuliani and New York State governor George Pataki, the president told reporters, “an act of war was declared on the United States of America.” On September 15, he elaborated: “We’re at war. There has been an act of war declared upon America by terrorists, and we will respond accordingly.” He encouraged people to “go about their business . . . but with a heightened sense of awareness that a group of barbarians have declared war on the American people.”

But from the beginning, it was understood that the War on Terror would be different from the many that preceded it. The Holy Grail of our new war was not territory, but intelligence. The attacks were immediately constructed as an intelligence failure. ABC News called 9/11 “a desperate failure of intelligence in both the human and technical area.” The Washington Post described it as “a massive intelligence breakdown.” Leon Panetta, former chief of staff for President Bill Clinton and later director of the CIA and secretary of defense for President Barack Obama, said it “was clearly a colossal failure of our intelligence community.” Vice President Dick Cheney’s infamous warning on September 16—that the War on Terror would take the United States to “the dark side,” working “in the shadows in the intelligence world”—offered a glimpse into the foundational objective of the war: what the NSA called “Information Dominance.”