In June 2015, retired Lt. Gen. Michael Flynn took a little-noticed trip to Egypt and Israel, paid for by a U.S. company he was advising. The company hoped to build more than two dozen nuclear plants in the region in partnership with Russian interests.

Flynn’s quiet involvement in that project — and his failure to disclose his ties to the effort — could complicate the legal issues facing President Trump’s former national security adviser, who has signaled he may be willing to cooperate with special counsel Robert S. Mueller III.