But there is a broader mistake in Johnson’s speech and the reaction to it. This error lies in seeing our era of lesser civil liberties as stemming from al-Qaida in particular. Al-Qaida was merely the symptom of two larger changes in world affairs. The first is the advance of weapons technology, which has made it easier for foreign terrorist organizations to miniaturize, hide, transport, and use dangerous weapons against civilian targets. And the second is globalization, which has thrust the United States into the affairs of unstable countries with murderous conflicts, putting it in the cross-hairs of unhappy groups., These two factors have made it impossible to go back to the era before 9/11.

Ordinary law enforcement methods are not effective against foreign terrorists in the modern era because foreign terrorists can train, recruit, obtain weapons, and hatch their plots in foreign countries with weak governments that cannot fully control their territory, making it impossible for the United States to demand extradition or conduct joint law enforcement operations. This puts the United States to the choice of either waiting for an attack to take place and hoping to thwart it at the last moment, or launching preemptive military operations abroad. In light of the destructiveness of the kinds of modern weapons that could be used against us — including chemical and biological variants — the choice is not very difficult.

The Clinton administration recognized these problems in its time, firing cruise missiles at al-Qaida camps in Afghanistan in 1998, and at a plant in Sudan thought to be used to manufacture chemical weapons for al-Qaida. The Clinton officials did not detain foreign terrorist suspects indefinitely, but they did ship them off to countries that would take care of them, one way or the other.

The Bush administration took the Clinton approach to its logical conclusion by fully militarizing counterterror operations. Realizing that security threats could come from any foreign terrorist organization, not just al-Qaida, it insisted on the president’s broad authority to counter any security threat, rather than relying solely on the AUMF. That is also why the Bush administration supported new laws, including the FISA Amendments Act and the Patriot Act, which enabled intelligence and law enforcement authorities to respond to, and take advantage of, new technologies. These statutes will remain on the books long after al-Qaida is vanquished.

The Bush administration also put into place institutional changes. It expanded the paramilitary arm of the CIA, revitalized the military’s special forces, reorganized intelligence gathering, and launched the drone program. These changes will also outlast al-Qaida. The idea of calling the conflict with al-Qaida a “global war on terror,” rather than a war on al-Qaida or a war on Islamic extremism, reflected the sense of a new era of wider danger. And while the Obama administration rejected the rhetoric, it has embraced most of the Bush administration’s legal and institutional initiatives.

The United States may finally land a decisive blow against the core of al-Qaida, and could conceivably even lop off its many hydra heads around the world. But the United States will always be vulnerable to foreign terrorism. The 9/11 attacks merely woke us up to this amorphous threat. To protect the country, the public and the political class acquiesced in expanding presidential power and limiting civil liberties. These changes will remain with us as long as the threat does.

Eric Posner, a professor at the University of Chicago Law School, is a co-author of “The Executive Unbound: After the Madisonian Republic” and “Climate Change Justice.”