Virginia Tech, Fort Hood, Tucson, Aurora, Newtown. And now Washington.

At least 12 people were killed during a mass shooting Monday morning at the Washington Navy Yard, and the toll could climb higher. A gunman is also dead.

Another rampage. This one, for me, very close to home. My kids and I biked to the Navy Yard on Saturday.

How can this country tolerate another mass shooting after we’ve endured so many others? And why have we allowed ourselves to grow accustomed to this awful bloodshed? Because that’s what these slaughters have become: practically routine.

“How many this time?” we ask as we watch the number of dead and injured climb on TV or Twitter.

Columbine principal Frank DeAngelis spoke with Nia-Malika Henderson on the emotions that mass shootings spark for him, and how he recovered after the 1999 tragedy at his Colorado high school. (The Washington Post)

Even the folks inside Building 197, home to the Naval Sea Systems Command, knew what was happening. Patricia Ward, who works for the Navy, was on her way to breakfast with two friends when they heard the gunfire.

One of Ward’s friends started to ask, “Was that a gunshot?” But she was interrupted by the sounds of “BAM, BAM, BAM, BAM, BAM,” Ward said. “We knew it then,” Ward told The Washington Post’s Steve Hendrix. “We just started running.”

About 16,000 people work at the Navy Yard. Building 197 is full of folks who do the paperwork behind the Navy’s fleet. Ordinary people doing ordinary jobs were suddenly confronted with unthinkable carnage.

We’ve been here before so many times. And each time, we wonder whether this is the mass shooting that will finally wake us from our numb indifference.

It didn’t happen after the 2007 Virginia Tech massacre, when a student unleashed an attack that left 32 dead and more than two dozen wounded. It didn’t happen after the Fort Hood shooting, when an Army psychiatrist opened fire on dozens of soldiers in 2009, killing 13 and injuring 30. It didn’t happen after the 2011 assault in Tucson that killed a federal judge and left then-Rep. Gabrielle Giffords (D-Ariz.) with brain damage. It didn’t happen after the most heartbreaking mass shooting of all: the one last year that took the lives of 20 first-graders at Sandy Hook Elementary in Newtown, Conn., as well as six others.

After Newtown, it took a little longer for our collective indifference to return. But not even the pleas of grief-stricken parents who’d lost their children could make a dent in the opposition to any restrictions on the sales of semiautomatic weapons.

Our love affair with violent entertainment remains unshakable. Bloody movies still command huge audiences every weekend. Violent video games still generate billions in sales annually.

And gun sales have soared. Background checks for gun sales numbered almost 20 million last year, about 20 percent more than the year before.

But people have always had guns in America, and kids have always played violent games — if not “Call of Duty,” then cops and robbers. So what explains the fact that we have averaged one mass shooting a month in this country since 2009? That’s 43 shootings in which more than four people were killed in the same incident in the past four years, according to a study released this year by Mayors Against Illegal Guns.

We’ve gotten so used to mass shootings that we now tick off only the really big ones. The Oikos University shootings didn’t even register on the national radar. What? When? It happened at a Korean Christian college in Oakland, Calif., just last year. Seven of 10 people shot there died.

And when these happen, we as a society want to be thorough and examine all the things wrong that led up to an explosion of rage articulated in shrapnel.

There’s the lack of access to mental-health services. There’s the proliferation of violent video games. There’s unemployment and recession and the cruel death of the middle class. There is an epidemic of post-traumatic stress disorder from two wars and countless traumas.

But people have become embittered or disgruntled or even murderously angry ever since we walked upright.

There is a difference now: We have weapons readily available that can kill lots of people in a very short time, and we’ve woven the meme of mass shootings into the fabric of our society.

Even after all those little first-graders were shot in their classroom in Newtown and Giffords gave many passionate and difficult speeches about gun control, Congress didn’t have the will to decide that killing machines — assault weapons — should be restricted in any way.

Legally, we had a 10-year hiatus from them when the federal ban on assault weapons was enacted. But when it expired in 2004, our elected officials let it go.

Since then, we’ve decided that assault weapons are part of our culture. You don’t find them just in video games and movies: You can buy shower curtains and necklaces decorated with silhouettes of AK-47s.

When it comes time to seriously talk of banning them, we just refuse to go there. And if it weren’t for their easy accessibility, these expressions of rage would end in far less bloodshed.

Apple pie, baseball and mass shootings? No. We can’t let slaughter become part of the way we define ourselves.

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