Lack of provable corrupt intent (due to there being no crime to cover up) is what kept Mueller from being able declare criminal conduct by Trump. It worked for McCabe in this instance.
Barr stated May 20, 2019:
"Attorney General William Barr said that his handling of the Mueller report and its aftermath is rooted in a desire to defend the power of the executive branch rather than personal support for President Trump.
“I felt the rules were being changed to hurt Trump, and I thought it was damaging for the presidency over the long haul,” Barr told The Wall Street Journal in El Salvador in an interview published Monday, where he traveled last week to boost support for Trump’s policies toward the violent street gang MS-13.
“At every grave juncture the presidency has done what it is supposed to do, which is to provide leadership and direction,” Barr added. “If you destroy the presidency and make it an errand boy for Congress, we’re going to be a much weaker and more divided nation.”
Everyone who wants justice for this needs to temper expectations. Durham has been appointed for just nine months. These are heads of intel, FBI, and Rosenstein's DOJ; they're not stupid people who threw down trails of indictable breadcrumbs and we won't get everyone we want. McCabe is still under investigation, along with Comey, Brennan, etc.