Weissmann was involved long before Mueller chose him.
August, 2016: Ohr met with Justice officials again, who asked him to conduct a briefing to include others. At this briefing Ohr expressed the same concerns regarding conflict of interest and of bias.Present at the meeting were Weissmann,; Bruce Swartz; and Zainab Ahmad, also future member of Mueller's team and future prosecutor against Michael Flynn.The significance of Ahmad and especially Weissmann is that before having joined the Special Counsel team, they already knew the bias of the Dossier.
Yet, after joining in the investigation with Mueller, they continued basing their case on this Dossier, though they didn't openly admit to it. The FBI presented it as verified, deceiving the FISA court, violating the regulatory procedure (the Woods procedure), which became the subject of investigation in and of itself. The higher ranking individuals signed off on it,McCabe, for instance. Mueller knew this, and conducted the case regardless.
One of those who had deceived the FISC was John Carlin, of the DOJ National Security Division. He did not inform the court there was an audit ordered by Admiral Rogers of the agencies. After deceiving the court, Carlin announced his resignation, which would become effective on Oct. 15, 2016.
This was followed at the end of September or early in October by a meeting with Strzok, Page, and Justice Department (DOJ) members of the criminal division,Bruce Swartz, Zainab Ahmad, and……..Andrew Weissmann, discussing the Dossier.
November 8, 2016: Trump wins presidential election. In the meantime, Weissmann, a donor to her campaign, attended Clinton’s election-night party in NYC.Remember, also, in August he had been briefed by Steele on his dossier.In early 2017, Weissmann had also been revealing things from the Dossier to Washington reporters.
According to the Conservative Tree House:
“The April 12, 2017, Associated Press article reported that DMI (Manafort’s company) records showed at least two payments were made to DMI that correspond to payments in the black ledger.”
They didn't bother to mention it was WEISSMANN who had met with the Media a day before the publication of those articles, advising them, something filed by the FBI on April 11, 2017, that the AP (Media):
"were advised that they appeared to have a good understanding of Manafort’s business dealings."
Furthermore, those AP reporters were connected with Fusion GPS, one of whom, Chad Day, was also associated with Steele. According to the Conservative Tree House:
"Those AP reporters are almost virtually guaranteed to be the same AP reporters that are participants within the Fusion GPS network; and the same AP reporters who collaborate with Andy Weissmann et al. These endless media scribes were willing participants within the 2015/2016/2017 plot, plan and execution; and as such they are clearly acting/writing to protect themselves and their interests."
Weissmann had shown them documentation, and they talked about gossip Manafort used "some of the money from shell companies to buy expensive suits.” Manafort's indictment mentioned just such suits.