Turn on the news.

We've become far too used to that sentence. It usually means something horrible has happened. We heard it when O.J. Simpson was being chased by police cars. We heard it when planes flew into the World Trade Center.

We heard it Friday, when a 20-year-old gunman walked into a Connecticut elementary school and began firing, doing something unimaginable: killing innocent children, possibly all first-graders.

When stories like these happen, they are marked not just by tears, fury, finger-pointing and hand-wringing, but something else: a noticeable shift in national attitude.

And while it is still too early to fully measure the impact of the Sandy Hook tragedy, you know, in your heart, something here has changed for good. We were already a nation that over-worried about its children's safety. Now, no elementary school will be considered off-limits. No age group too young. No location too innocent.

What place is safe anymore?

What Adam Lanza did with his demented soul and his loaded guns was bump American fear that much closer to the red zone. The calls for school security will now -- and for the foreseeable future -- be elevated. The scrutiny over who gets into school buildings will forever be heightened.

And the sense that certain places are always safe -- that even that most evil wouldn't dare come here -- is forever shattered.

Turn on the news.

No, it was not the first school shooting. Not even the deadliest in this country. The Virginia Tech tragedy took more lives. And here in Michigan, there was a worse massacre of students, when a farmer named Andrew Kehoe blew up the school in Bath Township, near Lansing. He killed 44 people, wounded 58, and then, like Lanza and so many cowards before him, killed himself.

That happened 85 years ago. So we can't say senseless violence is new. But in the age of the Internet and 24-hour TV news, where images are instant and nonstop, it was the faces of frightened children and gasping adults that will stay with us for a long time.

That and the ages. These kids were 6? Seven? It is horrible enough to hear college students recalling a massacre. Or teenagers detailing murder at a movie theater. But the young, squealing voices of the Sandy Hook Elementary children describing the terror they felt was almost ... surreal. You wanted it to stop. You couldn't bear to hear such innocent faces talking about gunshots and fear and teachers making them close their eyes and hold onto one another as they ran out.

That type of horror you expect to lament in a war. When it happens at 9:30 a.m. in an upscale Connecticut grade school, there are no words.

But there is a reaction.

And it doesn't go away.

The morning of the shooting, I was traveling through an airport. In the security line, I got stuck behind a mother who was placing at least 10 items on the metal detector belt: bag, child's bag, coat, child's coat, stroller. As I stood there, tapping my foot, I thought back to how Osama bin Laden created all this. Little such security existed before al-Qaida's diabolical Sept. 11, 2001, attack, and little has dissipated since. There has not been a repeat act on our shores. Yet we still go through this preventative drill, flight after flight -- 11 years later.

What similar changes are likely in the wake of this latest tragedy? Will armed guards be the norm at elementary schools? Will parents decide where to enroll their children based on the level of gun-wielding security?

Surely, the debate will rage over whether more guns or fewer guns would have made a difference here. And a small minority will point out that when something like this happened in a grade school 16 years ago in Dunblane, Scotland, the entire United Kingdom banned handguns.

Expect no repeat here.

But something will give. In a nation that can't agree on much, we all hold hands over the preciousness of childhood innocence. Every parent squeezed his or her child a bit tighter Friday night, and every one will worry a bit more when the school bell rings Monday morning.