The allure of a Mueller report lies in its imagined promise of a single, definitive truth capable of cutting through the haze of lies, confusion and “alternative facts.” But Mr. Corsi’s and Mr. Papadopoulos’s antics are a warning that this hope will inevitably fall short. Conspiracy theorists and prosecutors live in different worlds: The first, unmoored from truth; the second, devoted to proving facts beyond a reasonable doubt. Mr. Mueller has the power to charge Mr. Corsi for lying; he has already done so to Mr. Papadopoulos. Rather than crumbling, though, their falsehoods have continued to spread and grow —...