Executive Privilege and Individuals Outside the Executive Branch [October 9, 2019] [open pdf - 578KB]
From the Document: "White House assertions of executive privilege for presidential communications have historically been confined to individuals who were executive branch employees when those communications occurred. While the idea that executive privilege could extend to individuals outside the executive branch predates the Trump Administration, it appears that recent testimony by Kris Kobach, former Kansas Secretary of State, and Corey Lewandowski, former manager of Donald Trump's 2016 presidential campaign, are likely the first times the executive branch has actually made such an assertion to Congress."
CRS Insight, IN11177
Congressional Research Service: https://crsreports.congress.gov/