President Donald Trump didn’t know that then-National Security Adviser designate Michael Flynn had spoken about sanctions with the Russian ambassador to the United States until weeks later.

“He was not aware, as he is not back-briefed on every conversation that his national security team has, or other staffers. They were performing their duties, as other people were in terms of getting up to speed, conveying to counterparts and previous members of their team,” White House press secretary Sean Spicer said at a press conference Tuesday.

Flynn spoke with the Russian ambassador, and discussed sanctions, shortly after the Obama administration imposed sanctions on Russia on Dec. 29, 2016.

Then-acting Attorney General Sally Yates told the White House that Flynn may have misled members of Trump’s administration about the contents of his call with the ambassador on Jan. 26, Spicer confirmed Tuesday.

Eighteen days after the White House learned Flynn had misled them, Flynn resigned on Feb. 13.

“He was made aware of it — once White House counsel briefed him on concerns the Department of Justice had,” Spicer continued. “And at that point, as I mentioned, what he asked and what he believed at the time and was confirmed by White House counsel, was that there was no legal issue here. Discussing the issue didn’t violate anything. It was appropriate in the normal course of action to discuss that. He immediately asked the White House counsel to further confirm what his instincts were at the time.”

Spicer went on to say that, “as far as we are aware, that is an isolated incident,” after being asked if the White House would undertake an effort to clarify if anyone else had spoken about sanctions with Russia.