Erik Prince, the founder of private security company Blackwater, has found himself embroiled in special counsel Robert Mueller’s investigation of potential coordination between the Trump campaign and the Kremlin. During the campaign, Prince reportedly met at Trump Tower with Donald Trump Jr., operative George Nader, and social media specialist Joel Zamel to discuss a potential pro-Trump social media influence operation. He also met with Russian sovereign wealth fund manager Kirill Dmitriev during the transition period—a meeting reportedly planned to set up a backchannel between the Trump administration and Russia. Those revelations raise questions about his relationship to the Trump administration—questions...