Stephen Miller told Mueller about how Jared Kushner coordinated with data firm Cambridge Analytica: report
White House senior policy adviser Stephen Miller.

Among the revelations in the new BuzzFeed News document dump from former special counsel Robert Mueller's investigation is that White House adviser Stephen Miller gave Mueller's prosecutors information about President Donald Trump's son-in-law Jared Kushner's involvement in coordinating with Cambridge Analytica, as well as now-Trump campaign manager Brad Parscale:

Cambridge Analytica, an infamous big-data firm headed up by the powerful right-wing Mercer family, has come under scrutiny for its questionable use of data in political microtargeting strategies against people who may not have consented to the use of that data. The company shut down in 2018, although the Mercers have other businesses still operating that do essentially the same thing.