While a number of prominent Trump Cabinet officials have already left the administration, it was nonetheless surprising when UN Ambassador Nikki Haley announced Tuesday that she'll be resigning by the end of the year.

Haley had been a prominent adviser in shaping administration foreign policy in the first year and a half of Mr. Trump's term, although her influence has waned since Secretary of State Mike Pompeo and National Security Adviser John Bolton were appointed.

As ambassador to the United Nations, Haley represented the United States before the world. In losing Haley, Mr. Trump is losing one of his best advocates for an "America First" foreign policy. Her replacement will have to be confirmed by the Senate, meaning that Mr. Trump may have to turn to a crowd-pleasing candidate instead of a controversial conservative firebrand -- or family member.

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Here are the people who could potentially replace Haley:

Dina Powell

Powell appears to be a leading contender in the unofficial race to replace Haley. Mr. Trump told reporters Tuesday afternoon that he was considering Powell for the job. A current Goldman Sachs executive and former deputy national security adviser to Mr. Trump, Powell already has a connection to the president that could be a decisive factor. Although she served in the administration for less than a year, Powell was critical in crafting Middle Eastern policy, particularly with regard to building a friendlier relationship with Saudi Arabia.

Ivanka Trump

The president's daughter and her husband, Jared Kushner, have been key advisers during his time in office. Haley praised the two on Tuesday, even calling Kushner a "hidden genius." Mr. Trump floated the idea that he was considering his daughter as Haley's replacement Tuesday afternoon, telling reporters that she would be an "incredible" and "dynamite" ambassador to the UN. However, he also conceded that if he nominated her, it would be seen as nepotism. As rumors swirled around the internet, Ivanka Trump took herself out of the running shortly thereafter. "It is an honor to serve in the White House alongside so many great colleagues and I know that the President will nominate a formidable replacement for Ambassador Haley. That replacement will not be me," she wrote on Twitter. However, her recusal doesn't preclude Kushner from being nominated.

Joe Lieberman

The former Democratic and independent senator from Connecticut and Al Gore's 2000 running mate may not seem like a typical choice for the Trump administration, but CBS News' Major Garrett reports that Lieberman is being considered because he would support Mr. Trump's pro-Israel approach to issues related to settlements and security, lending bipartisan credibility to the president's hardline stance. As a former senator, Lieberman might have a relatively smooth confirmation process as well.