Stephen Schlesinger is a fellow at the Century Foundation and author of "Act of Creation" about the founding of the United Nations. The views expressed in this commentary are his own.

(CNN) The US Ambassador to the United Nations, Nikki Haley, is going through one of the roughest patches in her public career. She still appears on the front pages with pronouncements at the UN, but her star, which was burning so brightly in the first year of the Trump administration, is beginning to dim significantly in the second year.

Here are some of the things which have put a dent in her stature. Haley did not attend the summit in Singapore between President Donald Trump and Kim Jong Un. Though it's unclear whether she was included in preparations or even invited, her absence was quite noticeable. Haley had been one of Trump's first choices for a top-level foreign policy position, had been granted Cabinet-level rank by Trump as his UN envoy and tasked by him to push his "America First" policies at the UN. And, in fact, she led the fight in the UN Security Council to successfully impose stricter sanctions on North Korea, citing it as one of her accomplishments. Yet, in this, Trump's most important foreign policy foray of his presidency, she may have been left out.

Stephen Schlesinger

She also missed out on another symbolic moment in the Trump saga -- she did not attend the ceremonial opening of the US embassy in Jerusalem. She had championed Trump's decision to move the embassy against fierce opposition both in the UN Security Council, where her veto of a resolution condemning the event was a lone vote blocking it (14-1), and in the General Assembly, where only eight other countries backed her attempt to refute a similar critical declaration. Some 128 nations voted for it and another 56 nations did not vote or abstained. Afterward, Haley went to great trouble to hold a reception for those few countries that had supported Washington to emphasize America's anger over its treatment at the UN.

Most recently, upheavals in Washington have now left her as the odd woman out in Trump's foreign policy's team. This has been a remarkable turn-about for, in Trump's first year, Haley outshone Trump's Secretary of State Rex Tillerson, National Security Adviser H.R. McMaster and Secretary of Defense James Mattis -- all grey men with little visibility -- with her vivacity, her skill in the media and winning television personality. Indeed, she even appeared, at times, to be pursuing her own foreign policy at the UN due to the continuing distractions and personnel reductions at the State Department and Trump's focus on domestic matters. Time Magazine put her on the cover as one of the most important "women who are changing the world."

But over the last several months, the President has replaced two of his three top national security figures -- John Bolton as the new National Security Adviser and Michael Pompeo as the new Secretary of State. These two men are hard-headed bureaucratic in-fighters -- Pompeo a former CIA director and congressman of deeply conservative convictions and Bolton a far-right ideologue. Both are also savvy operators in the media and are based in Washington DC, making them closer to Trump than Haley is. Trump, indeed, has said he likes Pompeo's manner and, while Bolton has no intimate ties to the President, he is just down the hall from Trump in the White House. Neither man is likely to give Haley any further free rein at the United Nations.

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