There has been a great effort this week to come to grips with the American left's reaction to the Tucson shooting. Paul Krugman of the New York Times and its editorial page, George Packer of the New Yorker, E.J. Dionne of the Washington Post, Jonathan Alter of Newsweek and others, in varying degrees, have linked the murders to the intensity of opposition to the policies and presidency of Barack Obama. As Mr. Krugman asked in his Monday commentary: "Were you, at some level, expecting something like this atrocity to happen?"

The "you" would be his audience, and the answer is yes, they thought that in these times "something like this" could happen in the United States. Other media commentators, without a microbe of conservatism in their bloodstreams, have rejected this suggestion.

So what was the point? Why attempt the gymnastic logic of asserting that the act of a deranged personality was linked to the tea parties and the American right? Two reasons: Political calculation and personal belief.

The calculation flows from the shock of the midterm elections of November 2010. That was no ordinary election. What voters did has the potential to change the content and direction of the U.S. political system, possibly for a generation.

Only 24 months after Barack Obama's own historic election and a rising Democratic tide, the country flipped. Not just control of the U.S. House, but deep in the body politic. Republicans now control more state legislative seats than any time since 1928.