Tarazi’s suit is very defensible by Geller.
Most of the advocacy he complains about is inarguably protected. His complaint that Geller falsely stated that he was paid by CAIR conflicts, thematically, with his complaint that Geller wrongly called CAIR a criminal organization. After all, if (as he suggests) CAIR is a perfectly benign organization, how can it be defamatory to suggest that he was paid by it?
Finally, what appears at first glance to be the most serious allegation — that Geller falsely accused Tarazi of perjuring himself about whether he was paid by CAIR — loses most of its steam when you see that Tarazi is accusing Geller of saying that others are reporting that Tarazi perjured himself.
Even if that’s read as a false assertion of fact by Geller — which is far from certain — Geller can defend it if she can establish a basis for believing that he was, in fact, paid by CAIR. Moreover, if she can establish that he was a public figure, generally or for a limited purpose, she can prevail by showing a lack of malice. The game-plan for defending a case like this is clear, to any reasonable lawyer.