General Discussion

Mueller actually indicted several people, who took a plea or were found guilty including Manaford. Even though hidden by Barr's lies, the conclusion seemed to be there was ample evidence that Russia did interfere against HRC for Trump, but it was not clear they had enough proof that Trump colluded. (Note the latter was when he was President - so it is a pretty damning report, much of which was not made public.)

For Brennan in 2016, it would have been negligent to NOT pursue foreign interference. Not to mention, the Obama administration tried to make a bipartisan joint statement on intelligence with the Republicans, but McConnell refused. The statement put out before the election carefully limited itself to Russian interference, not collusion with Trump and his campaign.

If anything, a case could be made that the Obama administration was extremely careful in not accusing Trump before the election. This even as Manford was doing some pretty suspicious stuff. The campaign also was involved with Cambridge Analytics using Facebook data and some of that data was rumored to have sent to Russia. If so, that data may have helped the troll farm target people on Facebook with lies.