As with so many other logistical issues, courts disagree about when litigants must provide evidentiary support for withholding their protected communications. Most courts require such evidentiary support only after an adversary challenges the litigant's privilege log. See, e.g., Fid. & Deposit Co. v. Travelers Cas. & Sur. Co., Case No. 2:13-cv-00380-JAD-GWF, 2017 U.S. Dist. LEXIS 84070, at *9 (D. Nev. May 31, 2017) (explaining that "it may be necessary to supplement the privilege log with affidavits or declarations if the basis for the claim of privilege cannot be adequately assessed from the privilege log").
But other courts are more demanding. In Crumpley v. Associated Wholesale Grocers, Inc., Case No. 16-2298-DDC-GLR, 2017 U.S. Dist. LEXIS 178300 (D. Kan. Oct. 27, 2017), defendant supplied a supporting affidavit after earlier submitting its privilege log. The court bluntly noted that defendant "puts the proverbial cart before the horse." Id. at *6. The court pointedly emphasized that "[o]ur cases have repeatedly held that the privilege log itself must contain competent evidence," and that "[s]imply attaching an affidavit to the response to a motion to compel misses the point of privilege logs." Id.
Most courts do not require simultaneous evidentiary support along with privilege logs. Such an approach seems to be a waste of resources -- requiring the withholding litigant to support privilege claims that the adversary may never challenge.