The news that the new George W. Bush Presidential Center on the SMU campus was briefly locked down on Saturday afternoon after a visitor saw a man with a gun sitting outside the building excited almost no attention at all in the media, meriting only a brief mention on the Dallas Morning News website. This was appropriate, since the weapon turned out to be a toy gun and the museum quickly resumed its normal operations.

For those of us who were caught up in this micro-event, however, it may take a few days to fully catch up to normal again. My wife and daughter and I, along with our friends Lawrence and Roberta Wright, had just passed through the metal detectors and bought our tickets and were standing in Freedom Hall, a big limestone atrium flooded with natural light. Above our heads, LED projectors presented shifting wrap-around images of a West Texas landscape. The place was crowded, and there was a long line of people waiting in the atrium for audio headsets.

Larry remembers hearing someone shout “Active shooter!” (See his New Yorker blog post about the incident here.) I remember only a strange, silent warping of reality. A woman in front of us collapsed to the floor. Her face was pale, her mouth open and quivering. Her husband grabbed her elbow. He seemed to be in a desperate hurry to pull her to her feet and get out of the building. Nobody said, “Get down!”, or at least nobody that I heard. But suddenly that’s what the hundred or so visitors in Freedom Hall did, none of us questioning, all of us acting in terrified compliance with some unheard directive.

Sue Ellen and Charlotte and I ducked behind a pillar, facing the entrance to the library. Larry and Roberta were across the room, huddled with most of the others against the wall, clearly vulnerable in that open space to attack from any direction, in any form. The employees in the circular wooden ticket booth in front of us had dived for cover as well.

No one spoke. There were people praying, and people crying. But nobody really asked what was going on. That was maybe the oddest thing to me: we all knew what was going on. This was less than a month after the Boston Marathon bombings. It would turn out to be the day before gunmen opened fire on a Mother’s Day parade in New Orleans. This was the attack we had been waiting for, preparing ourselves for, since 9/11. For me, at least, there was no sense of surprise, no sense of unfairness. The Bush presidential museum seemed a natural enough place for somebody to target, and I felt negligent for dropping my guard and blithely bringing my family here without imagining beforehand everything that could go wrong and forming some kind of escape plan.

“I knew this was going to happen,” Charlotte said. She was whimpering in fear but she said this not as an existential complaint but just as a lucidly-stated fact. She’s 29 and has lived for half her life with terrorism as an ominous background threat. I told her nothing was going to happen, but I couldn’t get the right inflection into my voice to keep my reassurances from sounding anything but rhetorical.

“I want to get out of here,” she said. I did too, but since we didn’t know what direction the attack would be coming from it made more sense to stay where we were. Also, I’m not sure that what made sense or not had anything to do with our static cowering. The instinct to remain part of the herd was powerful. We were all mute and enervated, waiting for someone who knew what was going on to speak up and say something. But no one spoke, and there was no one to give orders or even offer informed opinions.

I liked our place behind the pillar. If there was a bomb, and the explosion came from the interior of the museum, we would be in good shape. But I was convinced that if it turned out there was a methodical shooter or team of shooters we had to make a break for it toward the front of the building. It seemed to me the best escape route would be toward a doorway to the right—to a set of galleries my official George W. Bush museum map labeled “A New Call to Service,” “Leading on the Issues,” and “Acting with Compassion.”

I had mentally rehearsed similar scenarios, long before this moment. We all have. Do I stay where I am and hope for the best? Do I run? Do I fight? Though this would turn out to be only a dress rehearsal leading up to those decisions, I was surprised by how dread and calm could exist in my mind at the same moment, by how clearly I understood that our survival was dependent on cold calculation.

After a few static minutes had passed, two grim-looking SMU police officers advanced across the atrium with automatic weapons leveled, headed toward the interior of the museum. A guard from the private firm contracted to provide the museum with security cautiously crept forward from the other side of the room with a handgun. I was glad to see them, but there were only three of them, and I hoped that as they headed into a dark museum gallery they had a better idea than I did of the threat they faced.

But of course there was no threat. Nothing was happening. And after perhaps five minutes that fact became clear without anybody saying anything. There was no more coherent reason for it to be over than for it to have begun. In short order the moment of terror passed, the praying and crying tapered off, the ticket sellers reappeared at their booths. We debated whether or not just to leave but decided—perhaps as an act of bravado to convince ourselves we were not really as shaken as up as we felt—that we might as well see the museum after all. As we walked through the first galleries—“A Charge to Keep”, “Creating Opportunity”— I barely glanced at the artifacts. I was too concerned with keeping Sue Ellen and Charlotte within reach. Anyway, hanging chads and No Child Left Behind were a musty memory from the year 2000. But when we followed the winding corridor and found ourselves in front of the raw centerpiece of the museum, the twisted beams of the World Trade Center, there was no way to pretend that the present has any power to shield us from the past.