Article snippet: WASHINGTON — The decision by Deputy Attorney General Rod J. Rosenstein to appoint the former F.B.I. director Robert S. Mueller III as special counsel for the criminal investigation into Russia’s interference in the 2016 election has transformed the inquiry and increased the potential risk it poses to the Trump administration. Mr. Rosenstein, who was overseeing the investigation because Attorney General Jeff Sessions recused himself, had resisted pressure to take that step. But recent events — including President Trump’s firing of James B. Comey as F.B.I. director, in which Mr. Rosenstein played a role — made that resistance increasingly untenable. Here is what the appointment means. Mr. Rosenstein’s letter gave Mr. Mueller the authority to look into not only links or coordination between Russia and Trump campaign officials, but also “any matters that arose or may arise directly from the investigation.” And it included a reference to a Justice Department regulation that permits special counsels to investigate attempts to impede their inquiry — like obstruction of justice and witness intimidation. That mandate would seemingly give Mr. Mueller a writ, if he wants, to investigate whether Mr. Trump’s interactions with Mr. Comey amounted to obstruction of justice. Given the circumstances, “he is required to look” at whether there was obstruction of justice, said Julie O’Sullivan, a former federal prosecutor who teaches criminal law at Georgetown University. “He can’t i... Link to the full article to read more