As part of his investigation, Special Counsel Robert Mueller is examining the period of time last summer when President Trump appeared set on getting Attorney General Jeff Sessions to leave his post, several people familiar with the matter told The Washington Post.
Mueller is reportedly interested in whether this is part of a pattern of attempted obstruction of justice. Over the last few months, Mueller's investigators have been asking witnesses about Trump's state of mind in late July and early August 2017, as well as private comments he made about Sessions; they are trying to determine if Trump's goal was to oust Sessions so he could replace him with someone able to have control over the investigation into Russian meddling in the 2016 election and possible ties between the Trump campaign and Russian officials. Sessions has recused himself from the Russia investigation.
Trump has made his displeasure with Sessions known publicly through Twitter, and also behind closed doors; people who spoke to Trump told the Post he has called Sessions "Mr. Magoo," the bumbling old cartoon character. Trump has also reportedly said that throughout his career, he's hired the best lawyers, and now he's stuck with Sessions, who he doesn't view as very loyal. Sessions has told people close to him that Trump's words sting, but he refuses to resign. The Post also reports that earlier this month, to commemorate his first year as attorney general, senior aides gave Sessions a bulletproof vest with his name on it.