Early in his term, Trump’s briefers discovered that when his oral briefing included intelligence related to Russia’s malign activities against the United States, including evidence of its interference in US politics, Trump would often blow up at them, demanding to know why they kept focusing on Russia and often questioning the intelligence itself, multiple former administration officials said.

“The President has created an environment that dissuades, if not prohibits, the mentioning of any intelligence that isn’t favorable to Russia,” a former senior member of Trump’s national security staff told me.

In response, his briefers — who must make difficult judgment calls every day on which intelligence to highlight to the President — reduced the amount of Russian-related intelligence they included in his oral briefings, instead often placing it only in his written briefing book, a document that is provided daily and sometimes extended to several dozen pages containing the intelligence community’s most important information.

But his briefers discovered over time that he often did not read the briefing book, leaving him unaware of crucial intelligence, including threats related to Russia and other parts of the world.