ould the FBI have prevented the June 2016 massacre at Orlando’s “Pulse” nightclub ? Suspecting his radical Islamist sympathies made him a potential terrorist, they interrogated the killer, Omar Mateen, three times before his attack. But they could not indefinitely detain him on the basis of their suspicions, because of his constitutional right to a writ of habeas corpus.

This writ compels arresting authorities to present offenders before courts for judgment. How absolute is the right? Abraham Lincoln suspended it during the Civil War, claiming constitutional authority under Article I, section 9, which states habeas corpus can be suspended if “in Cases of Rebellion or Invasion the public Safety may require it.” Lincoln claimed the South’s rebellious secession justified suspension. The location of the clause in Article I implies Congress should do the suspending. But Lincoln argued that, in rebellion’s chaotic circumstances, neither Congress nor the courts could function effectively. Only the executive—the commander-in-chief—could expediently enact and enforce the suspension.

Lincoln was severely criticized at the time for this infringement of liberty. In 1861, Chief Justice Roger Taney (of Dred Scott fame) heard the case Ex parte Merryman while sitting in circuit in Baltimore. John Merryman had been detained, on Lincoln’s authority, for rebellious activity in Maryland. Taney ruled this unconstitutional, for only Congress could suspend the writ of habeas corpus. In a letter to Erastus Corning after the decision, Lincoln argued that this was a preposterous restriction of his powers as commander-in-chief: “Must I shoot a simple-minded soldier boy who deserts, while I must not touch a hair of the wily agitator who induces him to desert?… I think that in such a case, to silence the agitator (by putting him in jail) and save the boy is not only constitutional, but, withal a great mercy.”

Does any of this apply today, where not agitators against the Union but secret enemies of the whole country are involved? An armed attack by one or two terrorists hardly constitutes rebellion, or invasion as we normally understand the term. Then what is it? I suggest that it is a very unusual form of invasion, defined as a direct assault on the nation, within our own territory, aimed at defeating us in war. These attacks are not normal crimes of an occasional nature. They are inspired, if not directly organized, by a foreign enemy—ISIS—with the object of terrorizing us. If a fellow citizen inspired by ISIS attacks us, it’s treasonous rebellion. If a non-citizen, it’s ISIS’s way of invading the country from within. Both justify suspension of the writ.

This is an unusual application of the clause, but we face an unusual enemy possessed of unusual cunning. ISIS knows we are hamstrung by our rigid view of rights. They are undoubtedly aware that the Supreme Court insists authorities wait for a “clear and present danger” before acting to prevent even the worst crimes, including rebellion. This harmful view ties the hands of law enforcement, even when substantial evidence exists of an intended crime. In dealing with an enemy like ISIS it could be fatal. It has already had devastating effects in Orlando and San Bernardino.

ISIS is blatantly waging war on us. Do we still have the ingenuity and the will to defeat our enemy and save our country? It is hard to believe that a nation capable of saving the world from the Nazis in 1945, and from communism a quarter of a century ago, cannot meet this formidable new challenge. But success will require better thinking than we have demonstrated so far.