Looking for legal defenses of the Rick Perry indictment

I've posted below on why I think the Perry indictment is legally unsound -- but I want to make sure I'm not missing some important legal issues. Can anyone please point me to specific legal arguments explaining why Perry's behavior violates the specific statutes mentioned in the indictment (rather than general explanations of why the behavior was unsavory or ill-intentioned, or why there ought to be a law against it)?

The Perry indictment and the criminalization of politics

UC Irvine’s Rick Hasen writes at Electionlawblog: Texas Governor Rick Perry¬†has been indicted for coercion and abuse of power in a potentially politically motivated prosecution for actions Perry possibly¬†took out of political motivation to shut down possible politically motivated prosecutions. Got that? . . . Perry joins the list of other politicians prosecuted under controversial […]