Cambridge Analytica was relying on data pulled from millions of unwitting Facebook users to construct psychological profiles on people that could be used manipulate them in order to influence elections. Bloomberg was writing about Cambridge Analytica back in 2015 for working for the Cruz campaign. The Guardian and Politico also wrote articles about this in 2015. So mainstream journalists have known about this kind of election meddling before the election had even concluded, but only now has it become an "issue" after the DNC humiliation and the need to maintain Russia as the boogeyman.
https://melmacpolitics.com/2017/03/31/cambridge-analytica-arrives-in-australia/