Sam Clovis, a former national co-chairman of the Trump campaign, is one of three Trump figures known to have been contacted by FBI informant Stefan Halper during the 2016 presidential campaign. Clovis received an email, out of the blue, from Halper, whom he did not know, on August 29, 2016 — after Halper had been in touch with Carter Page and just before he contacted George Papadopoulos. Page and Papadopoulos were peripheral, sometime volunteer Trump foreign policy advisers, but they are key figures in the investigation into whether the Trump campaign colluded with Russia to rig the 2016 election. Clovis,...