Americans have much to be proud about in the aftermath of Monday's bombings at the Boston Marathon. The heroic responses by first responders and ordinary citizens in the moments following the two blasts that shattered a cherished day of celebration are both poignant and fascinating.

From the 78-year-old marathon runner who was blown off his feet and then got up and finished the race to the numerous tales of ordinary citizens tearing off their clothes to make tourniquets for the injured, we saw grit and resolve. They remind us that the human spirit is greater than any power that might try to force a retreat into the shadows of fear.

First responders are receiving well-deserved praise. The images of them, along with race workers and citizens, running toward the blast zone to help the injured are inspiring. Wednesday's reports that authorities are closing in on two possible suspects -- less than 48 hours after the incident -- demonstrate the efficiency and dedication of the world's best law enforcement network.

In the coming days, however, the focus of attention will shift toward this critical question: Could this attack have been prevented? Reviews and investigations surely will be launched. Is it possible to secure a 26-mile race course and ensure the safety of tens of thousands of runners and spectators? What about similarly packed public venues? We don't have those answers.

We do know that law enforcement has had great success in thwarting other planned attacks on U.S. soil, and that preventing them is an ongoing, 24/7 challenge. Sadly, we now live in a time when we must confront the inevitability of such events, and we may have to accept that heinous crimes like this will occur. Just the same, we must use everything available to us -- technology, manpower and our vigilance as individual citizens -- to help prevent them.