After days in which some Democrats and their supporters in the press assigned blame for the violence in Tucson on Sarah Palin, the Tea Party, Rush Limbaugh, and Republicans in general, President Obama says "none of us can know exactly" why accused killer Jared Loughner attacked Rep. Gabrielle Giffords and 19 others last Saturday.

"None of us can know exactly what triggered this vicious attack," Obama said.  "None of us can know with any certainty what might have stopped those shots from being fired, or what thoughts lurked in the inner recesses of a violent man's mind."

Later, the president stated flatly that a lack of civility "did not" cause the violence in Tucson.  His statement came amid mounting evidence that Loughner was not only not political in outlook but was severely mentally ill and that various authorities in the Tucson area were aware of his mental disturbance but did not take action to steer him toward treatment or have him institutionalized.

Obama's speech appears to undercut statements, made by some prominent voices in the media, pointing the finger of blame at several figures on the Right.  In the aftermath of Obama's speech, it is not clear whether the accusers, who include New York Times columnist Paul Krugman, DailyKos founder Markos Moulitsas, and MSNBC's Keith Olbermann, will now change their positions.

Obama was widely expected to avoid the issue of political rhetoric in the speech.  Instead, he devoted a significant amount of time discussing it.  His point seemed to be that the tone of the nation's political rhetoric did not cause the violence but that it should be changed anyway, as a way of honoring the victims of the Tucson attack.  "Let's remember," Obama said, "that it is not because a simple lack of civility caused this tragedy -- it did not -- but rather because only a more civil and honest public discourse can help us face up to our challenges as a nation, in a way that would make them proud.

Here is the lengthy portion of the president's speech touching on the political controversy:

When a tragedy like this strikes, it is part of our nature to demand explanations – to try to impose some order on the chaos, and make sense out of that which seems senseless.  Already we’ve seen a national conversation commence, not only about the motivations behind these killings, but about everything from the merits of gun safety laws to the adequacy of our mental health systems.  Much of this process, of debating what might be done to prevent such tragedies in the future, is an essential ingredient in our exercise of self-government. But at a time when our discourse has become so sharply polarized – at a time when we are far too eager to lay the blame for all that ails the world at the feet of those who think differently than we do – it’s important for us to pause for a moment and make sure that we are talking with each other in a way that heals, not a way that wounds. Scripture tells us that there is evil in the world, and that terrible things happen for reasons that defy human understanding.  In the words of Job, "when I looked for light, then came darkness."  Bad things happen, and we must guard against simple explanations in the aftermath. For the truth is that none of us can know exactly what triggered this vicious attack.  None of us can know with any certainty what might have stopped those shots from being fired, or what thoughts lurked in the inner recesses of a violent man’s mind. So yes, we must examine all the facts behind this tragedy.  We cannot and will not be passive in the face of such violence. We should be willing to challenge old assumptions in order to lessen the prospects of violence in the future. But what we can’t do is use this tragedy as one more occasion to turn on one another.  As we discuss these issues, let each of us do so with a good dose of humility.  Rather than pointing fingers or assigning blame, let us use this occasion to expand our moral imaginations, to listen to each other more carefully, to sharpen our instincts for empathy, and remind ourselves of all the ways our hopes and dreams are bound together… If, as has been discussed in recent days, their deaths help usher in more civility in our public discourse, let's remember that it is not because a simple lack of civility caused this tragedy -- it did not -- but rather because only a more civil and honest public discourse can help us face up to our challenges as a nation, in a way that would make them proud.  It should be because we want to live up to the example of public servants like John Roll and Gabby Giffords, who knew first and foremost that we are all Americans, and that we can question each other’s ideas without questioning each other’s love of country, and that our task, working together, is to constantly widen the circle of our concern so that we bequeath the American dream to future generations. I believe we can be better.  Those who died here, those who saved lives here -- they help me believe.  We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us.  I believe that for all our imperfections, we are full of decency and goodness, and that the forces that divide us are not as strong as those that unite us.

Reaction to Obama's speech has been almost universally positive.  What is less clear is whether the president's words will put an end to the narrative, started within hours of the shootings Saturday, that the accused killer was influenced by conservative rhetoric, or by the political atmosphere created by conservative rhetoric, and that therefore such rhetoric was to blame for the violence.