President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE reportedly tried to prevent Vice President Pence from appointing his chosen national security adviser, citing the staffer’s past opposition to Trump’s candidacy.

Axios reported Sunday that Trump was upset when he learned Pence was hiring Jon Lerner to advise him on national security and foreign policy. Lerner currently serves as a deputy for U.S. Ambassador to the United Nations Nikki Haley Nimrata (Nikki) Haley'The soul' versus 'law and order' Author Ryan Girdusky: RNC worked best when highlighting 'regular people' as opposed to 'standard Republicans' GOP lobbyists pleasantly surprised by Republican convention MORE.

The Washington Post reported last Thursday that Pence hired Lerner, and that Lerner would continue to work with Haley despite his new role advising the vice president.

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Prior to joining Haley’s team in the Trump administration, Lerner advised the super PAC supporting Sen. Marco Rubio Marco Antonio RubioOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Democrats step up hardball tactics as Supreme Court fight heats up Press: Notorious RBG vs Notorious GOP MORE’s (R-Fla.) 2016 presidential campaign.

He also worked as a pollster with the Club for Growth, a conservative group that ran anti-Trump ads during the 2016 campaign and has at times been critical of the president’s policies.

His past roles bothered Trump, Axios reported, citing three sources. He questioned why Pence would hire Lerner, and told chief of staff John Kelly John Francis KellyMORE to block the move.

The White House reportedly learned of the hire as Pence was traveling to Peru for the Summit of the Americas. After the vice president landed, he spoke to Trump and reassured him of Lerner's qualifications, Axios reported.

Pence is in South America for the gathering of leaders of the Western Hemisphere after Trump announced last week he would no longer attend. The White House said Trump would remain in the U.S. to coordinate a response to the recent suspected chemical weapons attack in Syria.

Pence's addition of Lerner to his national security team comes as Trump's new national security adviser, John Bolton, reshapes his team as well.