It was always an uphill struggle for Mueller, since collusion itself is not a crime. In other words, even if he could show that individuals in the Trump campaign had colluded with Russian agents to help elect Trump, that would be a serious political sin, but not a federal crime. Even if Mueller could prove that members of the Trump team had colluded with Julian Assange to use material that Assange had unlawfully obtained, that, too, would not be a crime. What would be a crime is something that no one claims happened: namely, that members of the Trump campaign told Assange to hack the Democratic National Committee before Assange did so. Merely using the product of an already committed theft of information is not a crime. If you don’t believe me, ask the New York Times, the Washington Post, the Guardian and other newspapers that used material illegally obtained by Assange with full knowledge that it was illegally obtained. Not only did they use information from Assange, but also from Chelsea Manning and from the stolen Pentagon Papers. The First Amendment protects publication by the media of stolen information. It also protects use of such information by a political campaign, since political campaigns are also covered by the First Amendment.
It is important to note that Special Counsel Robert Mueller does not have a roving commission to ferret out political sin, to provoke new crimes, or to publish non-criminal conclusions that may be embarrassing to the President. His mandate, like that of every other prosecutor, is to uncover past crimes. In Mueller’s case those crimes must relate to Russia. He also has the authority to prosecute crimes growing out of the Russia probe, but that is collateral to his central mission. In the end, Mueller should be judged by how successful he has been in satisfying his central mission. Judged by that standard and based on what we now know, he seems to be an abysmal failure.