Ronan Farrow reports at The New Yorker:
When I mentioned the White House’s role in escalating rumors of his demise, Tillerson appeared to have been waiting for the question. “Mm-hmm,” he said, nodding. “When you say ‘the White House,’ who are you talking about?” he asked. “The White House is comprised of how many people?” Hook, the director of policy planning, chimed in that the answer was perhaps in the thousands.
Tillerson waved him off. “But people that matter, people that might have an interest in whether I stay or leave, there’s about one hundred and sixty of them.” Tillerson leaned in and, for a moment, I realized that it must be unpleasant to be fired by him. “I know who it is. I know who it is. And they know I know.”
According to multiple individuals who had heard Tillerson speak of the matter behind closed doors, this was a reference to Trump’s son-in-law and adviser, Jared Kushner. Before Tillerson’s departure, tensions between the two men had been flaring regularly, often in the form of a public-relations proxy war.