When I first read about Joseph Stack flying a plane into an Austin office building which housed the local IRS office I pretty much saw him as a Tea Party terrorist. After reading the Joseph Stack Manifesto I have to admit that he does have some left-wing elements to his "ideology" but on balance he seems more like an ordinary "Joe" who has had a series of frustrating Kafka-esque experiences with the bureaucratic IRS. At the same time,there do seem to be some tea party types embracing him as an American hero after the fact.
In any case, even if this particular incident isn't the responsibility of someone clearly in the Tea Party camp, there have certainly been other warning signs that anti-Obama conservative backlash has been becoming more and more aggressive and has the potential for moving in violent directions. (see pray for obama and the murder of george tiller)
See also: I Am Not Saying Joe Stack Is A Teabagger, But He’s A Little Teaish By Casey Gane-McCalla