A press release here. I have not yet read the complaint, but assuming his tenure contract with Marquette includes standard AAUP protections for academic freedom, he has a good claim.
ADDENDUM: I'm astonished to see that Justin Weinberg (South Carolina) continues to assert, falsely, that Prof. McAdam's original blog post was inaccurate; in fact, it was almost entirely accurate. The faculty committee report from which he quotes is astonishing, a formal confirmation that Marquette University is not a serious university that values either academic freedom or free speech. (As an amusing aside, even the committee report acknowledges at the bottom of p. 152 that the existence of inaccuracies in the original blog post is irrelevant!) It as written as though there is some legal ambiguity about whether Prof. McAdam's extramural speech is legally protected by his contract with the university; there is not. It acts as though it is up to the committee to redraw the boundaries of academic freedom; it is not. If the contract incorporates the AAUP standards, then the matter is legally closed. Most astonishingly, it invents a new obligation, namely that when faculty speak extramurally, they "avoid recklessly causing [others] harm, even indirectly." It is a shame there won't be a photo of the look on the judge's face when he or she reads this interpretation of Marquette's contractual obligations to protect the academic freedom of Prof. McAdams. There is no extant interpretation of freedom of speech or academic freedom that would license such a restriction, and for the obvious reasons that it is too vague for anyone to be able to anticipate what speech it encompasses.
This is a good moment to remember how nonsensical the original characterization of this event--"powerful" tenured faculty member attacks "vulnerable" graduate student instructor--has clearly become. The "vulnerable" graduate student now attends a much better PhD program; the "powerful" tenured faculty member may lose his job or, more likely given that Marquette is pretty clearly in breach of contract, he will be forced into an early retirement with a settlement package.