As Nikki Haley sat by his side in the Oval Office Tuesday, President Trump announced that the United Nations ambassador is resigning at the end of 2018.

“She has been very special to me, done an incredible job,” Trump said of the former governor of South Carolina, adding that Haley is welcome to return to the administration in other capacities.

Haley was confirmed as U.S. ambassador to the U.N. shortly after Trump’s inauguration last year. From the beginning of her tenure, she was a fierce advocate of Trump administration policies, announcing the United States would be “taking names” of countries that did not support U.S. votes.

On her very first day as ambassador, Haley promised a “new day” under Trump’s America First policy. Initially seen as inexperienced in foreign policy, she soon was taken seriously by her fellow U.N. diplomats as she pushed through three sets of sanctions against North Korea and convinced China and Russia, both allies of Pyongyang, to agree to abide by them.

She spoke often of the need for reform within the U.N. and its peacekeeping forces, and frequently chastised U.N. agencies for taking anti-Israel stances. She pushed for Security Council resolutions imposing greater sanctions on North Korea, and chastised members who the administration suspected had been cheating.

“She was critical in ushering in U.N. reforms in partnership with the secretary general, and she took a thoughtful approach to peacekeeping and national security issues,” said Peter Yeo, an official with the U.N. Foundation. “There certainly were great areas of contention between the United States and the U.N. But she played a very important and constructive role.”

She became known for being a hawk on Iran and its regional aggression, a strong advocate of Israel and, working together with Secretary General Antonio Guterres, a force for cost-cutting.

Though Haley advanced Trump’s policies, she occasionally made public statements at odds with the White House and the president she served.

In December, she said that women who had accused Trump of sexual misconduct “should be heard.” When a White House adviser said Haley had been confused in prematurely announcing more sanctions against Russia, she said simply, “With all due respect, I don’t get confused.”

Haley’s ability to speak eloquently and forcefully on contentious issues fueled much speculation she has political ambitions beyond the U.N., possibly including a White House run. But Haley constantly denied it, saying she hadn’t given any thought to a presidential run.

Josh Dawsey contributed to this report.

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