Americans have become far too familiar with the carnage of bombings abroad. But the horrific terrorist attacks on the Boston Marathon have brought the bloodbaths associated with Baghdad, Kabul, and countless other cities abroad back to U.S. soil. Lost limbs, ball-bearing packed IEDs, mass casualties and amputations– all destroying what should have been a beautiful day of celebration and unity. It was an attack on the very foundation of who we are.

As a country, we will confront both our fear and rage together, knowing that there will be painful days ahead. But our immediate attention focuses on the action of the moment: Finding those responsible and preventing any further attacks.

There was rampant speculation in the minutes after the bombings on who was responsible. Putting aside the political proclivities of many obtuse commentators and their pretense of analysis, it is very likely we will soon know who the culprits are. Many investigative tools are at hand. With video footage from cameras and cell phones nearby, it may be possible to isolate terrorists from others in the crowd just before the detonations.

If they used stand-off devices requiring an electronic signal such as a cell phone call, or a timed device, it may be more difficult to trace video backwards and compile suspects. But there will certainly be a vast array of electronic data for federal authorities to analyze. And even if the explosive devices were simple designs, the bomb blasts suggest a level of expertise that requires training. They may have left behind essential clues.

Of course, time is of the essence. Law enforcement agents are working feverishly to identify the responsible parties to prevent their escape as well as the remote possibility of follow-on attacks. Right now federal and local agencies are compiling data, crunching numbers, and sending out teams to chase down every lead. From FBI agents to local cops, they will not rest until their mission is completed.

Boston is their town, too. They know the stakes.

It is also important to establish right away that there will be few security lessons to draw from the 4/15 attack. Crowds will always be at some level of risk in a free society, and there will forever be bloodthirsty villains who embrace the most depraved acts in pursuit of unthinkable evil. Planting simple but deadly explosive devices in a crowded public space will remain an option available to the sadists of Al Qaeda or the lunatic lone wolf anarchist.

When an individual or group plans to harm civilians, there are endless targets and limited protective resources. Many devastating plots require the least planning and expertise to conduct. A commando-style raid similar to the Mumbai attacks, for example, could only be averted before a shot is fired, or after many casualties.

There are simply too many ways to cause widespread harm, and terrorists only have to get through our defenses once.

That is not to say that nothing can be done. Already we know that police and first responders rushed to the scene and likely saved many lives. Nearby trauma centers in Boston may well have stopped horrific injuries from turning fatal. In a more remote area, further from help, more victims may have bled out from their wounds, and the mortality rate from the attack would have been higher. Boston’s emergency services performed with courage and skill.

But the uncomfortable truth is that, until now, America has largely relied on luck to avert other mass casualty attacks over the past four years. Both Faisal Shahzad, the Times Square Bomber of 2010, and Farouk Abdulmuttalib, the “underwear bomber” of 2009, were defeated by their own ineptitude. No expensive security procedure or highly trained agent prevented them from carrying out their attacks.

Despite this reality, soon the discussion about prevention will quickly turn political, and many elected officials will seize upon this horror to push agendas or grandstand against their opponents. The current swell of unity across America will fade into partisan bickering. But what matters is that the attack in Boston serves as a stark reminder that we remain under threat, and we must resist the temptation to trade liberties for the perception of security.

We cannot have perfect security, and we should not try for it.

And over the next few days, we must not allow the evil actions of a few to undo the accomplishments of those who have run marathons in the past and will do so in the future. There are few things more exhilarating, uniting, and beautiful than watching marathoners overcoming their limitations and fears. We must stand with them all, united by love of country, family, and God, with an indefatigable desire to defend our civilization.

While America cannot say this will never happen again, we can prove beyond the shadow of any doubt that we will never give in. We will gather our wounded, mourn our dead, tend to our neighbors, and ensure justice is done.

That is who we are, and that is who we will continue to be.