But, more fundamentally, the nihilism and the craziness and the destructiveness that we see going on with the "extremists" within the Party represents a fuller flowering of what the Republican Party establishment sowed and cultivated.
The Tea Party didn't even exist before Barack Obama became president. But by then we'd already had, thanks to this Republican Party, eight years of the most lawless and the most destructive presidency in history (with the possible exception of Buchanan's).
The Tea Party was not part of Congress until 2011. But by then, we'd already had two years of Republicans in opposition taking the unprecedented step of making it their top priority to make the new president fail, to prevent anything good from being accomplished even if that meant voting against their own ideas.
1) In its top-down (astro-turf) dimension, it represents the deliberate effort of the most cynical components of the right-wing force (like the Koch Brothers, who put forward the money to launch it, and like Rupert Murdock's news empire, which publicized it into prominence) to enable the Spirit of Destructiveness to take further possession of the Republican Party.
2) In its bottom-up (grassroots) dimension, it represents the harvest of all the hatred and fear and delusional beliefs that the Republican establishment (e.g. Newt Gingrich, Rush Limbaugh, Karl Rove) deliberately cultivated for years. They themselves may not be crazy, but their stirred up the pot, unleashing into the center of the Republican Party the kind of John Birch radical right energy that, in earlier eras, was kept in the background by the Republican Party and the conservative movement.