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WASHINGTON (CBSMiami) — The Trump administration faces a high-level shakeup after less than a month in office.

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The president’s National Security Advisor, General Michael Flynn, suddenly resigned late last night. That followed questions about his conversations with Russian officials during the presidential transition.

Gen. Flynn admitted he didn’t tell Vice President Mike Pence and other officials everything about those discussions.

He now becomes the shortest-serving NSC advisor in modern American history.

Keith Kellog, another retired 3-star Army general, will take over the job for now.

In Flynn’s resignation letter, he blamed the “fast pace of events” during the presidential transition for causing him to “inadvertently” leave out key details of phone calls with the Russian ambassador prior to inauguration.

Flynn had claimed that the two did not discuss sanctions, a potential violation of U.S. law.

Yet evidence surfaced Monday that the Justice Department had warned the White House last month that Flynn had deceived them about his contacts with Russia. However, Flynn was allowed to continue advising President Trump on sensitive national security matters.

Early Monday, the White House sent mixed signals about whether his job was in jeopardy.

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“Yes, General Flynn does enjoy the full confidence of the President,” said Counselor Kellyanne Conway.

An hour later, Press Secretary Sean Spicer released a contradictory statement saying, “The President is evaluating the situation.”

But it was Vice President Pence’s anger at Flynn’s deception that convinced Trump to reexamine his role. Pence had repeated Flynn’s misleading account in a January interview on CBS’s Face the Nation.

“They did not discuss anything having to do with the United States’ decision to expel diplomats or impose censure against Russia,” Pence said.

The president will now have to find a new national security advisor in the midst of global risks, including provocative actions by North Korea and Iran.

Retired LTG Joseph Keith Kellog, a national security advisor to the Trump campaign, will temporarily take over Flynn’s position.

He’s a candidate to permanently fill the job, along with retired Admiral Robert Harward, a former deputy Centcom commander, and former CIA Director David Petraeus, who will visit the White House later this week.

Less than two hours before the high-profile shake up, President Trump praised his staffing choices during the swearing-in of Steve Mnuchin as Treasury Secretary.

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“With this appointment I’m following through on my promise to appoint only the very best and the very brightest,” said the president at the ceremony.