What we're hearing: Haley discussed her resignation with Trump last week when she visited him at the White House, these sources said. Her news shocked a number of senior foreign policy officials in the Trump administration.
Background: Haley, the former governor of South Carolina, was easily confirmed four days after President Trump's inauguration in 2017.
She has overseen Trump's shift in dealing with the UN, including the U.S. exit from the UN Human Rights Council, which Haley called the organization's "greatest failure."
Worth noting: Haley wrote a public op-ed in September challenging the N.Y. Times' anonymous op-ed:
"I don't agree with the president on everything. When there is disagreement, there is a right way and a wrong way to address it. I pick up the phone and call him or meet with him in person."
"Like my colleagues in the Cabinet and on the National Security Council, I have very open access to the president. He does not shut out his advisers, and he does not demand that everyone agree with him. I can talk to him most any time, and I frequently do."