Once again we're left to ponder the unfathomable, this time from a quiet town in the wooded hills of Connecticut.

After apparently killing his mother, a 20-something gunman walked into Sandy Hook Elementary School Friday morning and shot  20 students and six adults before the killing finally ended when he turned the gun on himself.

News reports called it one of the nation's worst mass shootings. We're used to ranking such things now. In numbers, at least, we find clarity.

As of this writing, little is known about the shooter. (That's a sentence we've written before.) Not to worry. In the weeks ahead, reporters will write hundreds of stories about the gunman, and some type of consistent portrait will emerge.

Just don't expect to understand what he did on Friday. It will never make sense.

We'll learn more about the victims, too.

"The majority of those who died today were children, beautiful little kids between the ages of 5 and 10 years old," President Obama told the nation. Then he paused, maybe thinking of his own daughters, and wiped away a tear the whole country could feel.

Despite the stomach-turning regularity of mass shootings in America, we seem never to come closer to a national consensus on gun control and mental-health care. We're not likely to figure it out this time, either.

We'll come together to mourn and lower the flags, but in a few days the divisiveness that defines us now will be back and the politicians will reflexively move on from Sandy Hook Elementary to the fiscal cliff.

Or maybe not. Maybe this evil, more than all of the other mass murders, will move a president to do more than shed a tear. Maybe he'll lead a meaningful national response, and be joined by congressional leaders in both parties -- and by the governors, legislators and city leaders in all 50 states.

It will take that kind of leadership. Evil and mental illness are too common now, and they too easily end up being armed and deadly.

On Monday, parents everywhere will reassure their children that everything is OK, that nothing like what happened in Connecticut could happen here. But only the youngest will believe them. Their older brothers and sisters have already lost their innocence in the blur of headlines from Colorado and Virginia and, closer to home, Red Lake and Cold Spring.

Yes, dear children, it really could happen here-- or anywhere. It already has.