American Carnage: On the Front Lines of the Republican Civil War and the Rise of President Trump by Tim Alberta:
Trump sacked Comey on May 9, publicly citing Rosenstein's reasoning for doing so. Senior White House officials, including Pence himself, insisted to reporters that Trump had acted on the recommendation of Sessions and Rosenstein. They swore up and down that the president's decision had nothing to do with the Russia probe. Trump, however, would quickly undermine those claims--and sabotage his own stated rationale for dismissing the FBI director.
In the Oval Office a day later, Trump hosted two top Russian officials, Foreign Minister Sergey Lavrov and Ambassador Sergey Kislyak. The president called Comey "a real nut job," according to the New York Times, and told them of the FBI probe, "I faced great pressure because of Russia. That's taken off." (Trump also disclosed highly classified information about an operation targeting the Islamic State, according to the Washington Post. The only photos of the meeting were shared by a Russian state photographer; no American media were permitted.)