"Liar" and (in this context) "fraud" are protected opinion.

Here’s the relevant part of the Memo in Support to Dismiss (please excuse the formatting of the copy-paste from the PDF):

Most of the statements Plaintiff challenges are att acks upon the credibility of his claim to have “invented” email. These include, for example, several passages in which Plaintiff is called a “fake,” a “liar,” and a “fraud” who is advancing a “false,” “misleading,” or “bogus” claim of original inventorship (or words to that effect). (E x. A hereto, § I.) The First Circuit has routinely dismissed claims targeting such rhetorical hyperbol e on the grounds that the opinions do not imply any actionable misstatements of fact. See, e .g., Phantom Touring, 953 F.2d at 728 (statement that musical was a “fake” and “a rip-of f, a fraud, a scandal, a snake-oil job”; affirming dismissal on motion for judgment on plead ings); McCabe v. Rattiner, 814 F.2d 839, 842-43 (1st Cir. 1987) (statement that plaintiff wa s running a “scam”); Gray, 221 F.3d at 248-49 (2000) (statement that plaintiff “faked” his close ness to the president, which was deemed a “vague and subjective characterization about what h appened”); Freeman v. Town of Hudson, 849 F. Supp. 2d 138, 160-61 (D. Mass. 2012), aff’d, 714 F.3d 29 (1st Cir. 2013) (statement that plaintiff was a “liar”; recommending that motion to dismiss be granted).

Courts in other circuits have ruled similarly, reje cting defamation claims based on rhetorical attacks that constitute non-actionable o pinions. See, e.g., Underwager v. Channel 9 Australia, 69 F.3d 361, 367 (9th Cir. 1995) (statem ent that plaintiff was “lying” about his qualifications); Obsidian Finance Group, LLC v. Cox , 740 F.3d 1284, 1293-94 (9th Cir. 2014) (statements accusing plaintiff of “fraud” and “dece it on the government”); Doctor’s Data, Inc. v. Barrett, 170 F. Supp. 3d 1087, 1123-24 (N.D. Ill. 2 016) (statements that plaintiff’s scientific report was misleading, its test employed a “fraud,” and its lab was “shady”); Spelson v. CBS, Inc., 581 F. Supp. 1195, 1203-05 (N.D. Ill. 1984), aff’d, 757 F.2d 1291 (7th Cir. 1985) (statements describing medical practitioners as “ca ncer con-artists,” “cancer quacks,” and “unscrupulous charlatans” who commit “fraud” and p rovide “phony” medicine); Colodny v. Iverson, Yoakum, Papiano & Hatch, 936 F. Supp. 917, 923-25 (M.D. Fla. 1996) (description of plaintiff as a “fraud”); Gill v. Delaware Park, LLC , 294 F. Supp. 2d 638, 647 (D. Del. 2003) (accusation that plaintiff was a “liar,” which the court deemed a non-actionable “epithet”); USA Technologies, Inc. v. Doe, 713 F. Supp. 2d 901, 908 -09 (N.D. Cal. 2010) (statement that plaintiff engaged in “legalized highway robbery” and was a “k nown liar”); Rizzuto v. Nexxus Products Co., 641 F. Supp. 473, 481-82 (S.D.N.Y. 1986) (adve rtisements attacking competitor by using phrases such as “unscrupulous sales people lying,” “lying salesperson,” “rip you off, ” and “don’t be conned”); Boese v. Paramount Pictures Cor p., 952 F. Supp. 550, 554-57 (N.D. Ill. 1996) (statement that “[e]verybody lied, all the wa y down the line, and that came back to haunt them”); Thomas v. Los Angeles Times Communications, LLC, 189 F. Supp. 2d 1005, 1015-17 (C.D. Cal. 2002) (statement that plaintiff misrepr esented actions during World War II and taught a “sham” course; motion to strike under California anti-SLAPP statute granted); Faltas v. State Newspaper, 928 F. Supp. 637, 647-49, aff’d, 155 F.3 d 557 (4th Cir. 1998) (statements that plaintiff would “lie to suit her agenda” and would “present lies as truth”). These cases are consistent with the broader principle that “[t]he l aw provides no redress for harsh name-calling.” Flowers v. Carville, 310 F.3d 1118, 1127 (9th Cir. 2002).

I know it takes time to sit down and read the filings, but I’ve gone through them all and found them to be edifying; I’m not a lawyer but they’re written in pretty plain language. If you’ve got the time to spare, they’re well worth reading in their entirety. I figure everybody here is interested in free speech law in general and this case in particular, and the filings are interesting and informative on both those subjects.

(Tangentially: If you were to use the word "fraud" in a technical, legal context, there are circumstances where that might be considered defamatory. But that’s not what Mike (or the anonymous commenter quoted by Leigh) did; he used it in a conversational sense, in an article that was clearly expressing an opinion about a public figure citing known and undisputed facts.)