It was the sort of thing Americans have expected and dreaded ever since 9/11 shattered this nation's sense of security 12 years ago.
We have watched from a comfortable distance the human carnage from bombs detonated in Middle Eastern shopping districts, on buses there and in mosques. It was a matter of time, it seemed, before America would experience the horror firsthand.
Monday's bombing at the Boston Marathon that has taken at least three lives and injured more than 175 is not a first for this country. Friday will mark the 18th anniversary of the bombing by a home-grown terrorist of the Alfred P. Murrah Federal Office Building in Oklahoma City that took 168 lives. A year later, a bomb was set off amid crowds at the Olympics in Atlanta, killing two and wounding more than 100. More recently, police foiled bombings planned for New York City's subways and Times Square.
It is impossible at this point to know whether Monday's attack in Boston was an act of terrorism planned by foreign enemies of the United States, a domestic group or the work of an individual. Least of all do we know why someone would set out to murder and maim on such a scale.
This country has been numbed in recent years by mass murders by gunmen in movie theaters, in shopping malls, even in an elementary school. News of these mass homicides obscures daily murders in cities like Chicago, or Washington, D.C. And, yes, in Des Moines, where two men were shot and killed in recent days.
But nothing prepares one for what happened Monday, and the nation shares Boston's grief and horror. Because it occurred amid the historic marathon that draws tens of thousands of runners and spectators, the Boston attack struck a nerve across the nation. All eyes and thoughts and prayers are focused on Boston, and we are thankful for the presence of first responders, law enforcement and volunteers who rushed to the aid of victims.
The question is whether this was a rare exception or something we must brace for more often. Either way, this nation must remain alert to the possibility of such attacks and do everything to thwart them. But, like the people of Israel or Iraq who live with these threats every day, we must learn to move on without becoming hostage to forces that aim to invoke terror.