WASHINGTON — Secretary of State Rex Tillerson was on the verge of resigning this past summer amid mounting policy disputes and clashes with the White House, according to multiple senior administration officials who were aware of the situation at the time. The tensions came to a head around the time President Donald Trump delivered a politicized speech in late July to the Boy Scouts of America, an organization Tillerson once led, the officials said. Just days earlier, Tillerson had openly disparaged the president, referring to him as a “moron,” after a July 20 meeting at the Pentagon with members of...