Dist. Ct. did not err in granting defendant-employer’s motion for summary judgment in action alleging that defendant terminated plaintiff-employee in retaliation for publicly accusing defendant of tax fraud, where basis for Dist. Ct. order was its finding that plaintiff was collaterally estopped from establishing in instant lawsuit that defendant committed tax fraud, where Wisc. state court, in parallel conversion action brought by defendant against plaintiff, had previously found that defendant had not engaged in any tax fraud. State court ruling on tax fraud issue was dispositive in instant federal action since absence of tax fraud rendered instant lawsuit without merit, and Ct. rejected plaintiff’s claim that collateral estoppel did not apply since: (1) according to plaintiff, he did not have full and fair opportunity to litigate tax fraud issue in state court proceeding; and (2) as public policy matter, application of collateral estoppel would deter whistleblowers from bringing meritorious lawsuits.