Jacob Weisberg at Slate hits one important nail on the head, I think, but completely misses the point:
At the core of the far right's culpability is its ongoing attack on the legitimacy of U.S. government—a venomous campaign not so different from the backdrop to the Oklahoma City bombing in 1995. Then it was focused on "government bureaucrats" and the ATF. This time it has been more about Obama's birth certificate and health care reform. In either case, it expresses the dangerous idea that the federal government lacks valid authority.
When governments lose their legitimacy in the eyes of their constituencies, they are in trouble. They cannot blame a "venomous campaign" for this. The question is simply whether the U.S. government, which (a) is a democracy and (b) has a constitution, still (a) has the support of its population and (b) has governed the nation within the bounds of the constitution. That't the basis of its legitimacy, plain and simple. Many well-less-than-"venomous" critics of U.S. policy, from Noam Chomsky on the left to Ron Paul on the right, have argued trenchantly (they have convinced me!) that on everything from drug policy to the wars in the middle east, the U.S. government has overreached its authority. Those policies, foreign and domestic, are simply not legitimate. The invasion of Afghanistan was a war crime, etc.
The bailout of Wall Street (on the vaguely fascist and certainly corporatist principle, it would appear, that "gain is private, loss is public") did not help matters. The (to my mind weird) refusal to show the "long form" birth-certificate of the President in order to answer questions about his citizenship didn't help either. And, finally, the implementation of health care reform before the repeal of policies that have undermined the legitimacy of the government shows that Obama is trying, first and foremost, to maintain the power of the central government—though arguably only in order to continue to be an instrument of Wall Street.
To acknowledge Weisberg's comparison, we can ask wether the ATF's actions at Waco bolstered or undermined the legitimacy of the ATF and, by extension, the federal government.
None of this, of course, justifies Loughner. We're playing "the blame game", as Slate's editors have aptly put it. I am saying that if it is true that "anti-government, pro-gun, xenophobic populism made the Giffords shooting more likely" then it is also true that pro-government, anti-gun, multicultural populism (i.e., left-liberal orthodoxy), which naturally prompts ("draws the fire of" we would once have said without thiking twice) its equal and opposite reaction, made it more likely.
Obama explicitly set out to change America. Not all of America wants to change, and Obama has done it quite quickly (as the year end successes showed). He has also, I think, made the changes in an ill-advised order. He should have withdrawn two imperial armies first. He should have called off the war on drugs. This would have mellowed the tensions between "populist" left and right (and enraged elites on both sides). With this gentler, kinder, less intrusive, less aggressive and more "popular" state in place, he could perhaps have changed the health care systema and opened the borders to immigration. He could then have gone on to curtail the powers of the Fed and the CIA, the ATF and the FBI.
Perhaps we should remember that Obama did not bring a whole new state to Washington: he took over an existing one. He took over the state and its legitimacy in the condition that it had been left by George W. Bush. With that in mind, perhaps we can understand how he might have overestimated his legitimacy. The idea that the Federal Government of the United States of America lacks at least a measure of legitimacy is indeed a dangerous one. It is not, however, absurd, nor even wholly unfounded. And it's not news.