On the day Christina-Taylor Green was born, 19 men using four hijacked air buses left a pristine American morning forever stained with blood.

As she was entering life, the rest of us were absorbing a lesson in how mean life can be. We saw proud towers disintegrate like sand castles, mangled bodies pulled from rubble, people with tear-streaked faces holding up photos of missing loved ones. And there bloomed in us a sense of union strong as blood ties, a renewed reminder of who we are.

We are Americans. “All” of us.

For some, it was likely a revelation. After all, we are quicker to define ourselves in tribal terms than national ones. We are African-American women. We are Jews. We are Southerners. We are conservatives. We are Mexican immigrants. We are gays.

But the events of that baby’s birth day showed that others do not see the fine distinctions into which we put so much stock. That day they told us, with unmistakable clarity: you are all Americans, whatever else you are.

Christina-Taylor Green was shot Saturday at a supermarket near Tucson. She was among six people killed in the attempted assassination of Rep. Gabrielle Giffords, Democrat from Arizona. Fourteen others were wounded, including Giffords, who was shot through the brain. She is still fighting for life at this writing.

Her alleged assailant is Jared Lee Loughner, a 22-year-old Army reject kicked out of a community college in September for behavior his classmates found threatening and bizarre. Authorities say Loughner has left a trail of Internet postings suggestive of a disturbed loner given to incoherent rantings and a belief that he has powers of mind control.

It was probably to be expected that the political spin was in motion before the bodies had even cooled. Tea party activist Judson Phillips quickly deflected blame for the tragedy. Giffords, he reportedly noted on his website, is “a liberal,” but, he said, “that does not matter now.”

Of course, if it didn’t matter, he wouldn’t have mentioned it. “At a time like this,” he said piously, “it is terrible that we do have to think about politics, but no matter what the shooter’s motivations were, the left is going to blame this on the Tea Party movement.”

It would indeed be specious and simplistic to blame that movement for this massacre. That makes as much sense as Jerry Falwell blaming feminists and the ACLU for the 9/11 attacks or media reports blaming video games for Columbine. If authorities are correct, we already know who to blame for this: Jared Lee Loughner. And he seems to have been motivated less by politics than by mental instability.

That said, Phillips’ attempt at a pre-emptive defense suggests a certain guilt of conscience, a tacit acknowledgement that political discourse in this country has become a national disgrace, hateful, poisonous and coarse. And that the tea party movement bears a lion’s share of the onus for that. And that if the movement did not cause Saturday’s tragedy, it did create the atmosphere that made such a tragedy feel … inevitable.

It was not the seed, but it was the soil.

Media empires have been built and political careers advanced upon a kind of violent, proudly extremist rhetoric that has less to do with elucidating philosophical differences than with demonizing them, stoking division through hatred and fear of the other, whether the other be Mexican, Muslim, gay or a dreaded liberal. There is, we have been repeatedly told, a difference between people like that and “real” Americans.

Something to keep in mind as we mourn the dead, among them a 9-year-old girl who aspired to help the less fortunate. On the day she was born, we remembered something important about ourselves.

It was long forgotten by the day she died.