The thing that mandates impeachment at this point is using the NSA to shut down the Justice Department's investigation into the matters of spying. That, and the use of "signing statements" to unilaterally rewrite and disregard law. But at least until now there were options to investigate, and possibly take to court. That option is now being removed. Impeachment is the only reasonable result to this usurpation of legislative and now judicial power in the hands of the executive.