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US President Trump has threatened to replace Mathis' defense minister. He said he might leave as an opposition party, but Mathis has been a balancing act with emphasis on diplomatic solutions in the nuclear crisis last year.

It is Son Suk Min correspondent in Washington.

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"I do not know," Trump said in a CBS news program. "I do not know if he will leave." "I do not know if Mathis is leaving the cabinet," he said.

"Mathis is a good person, but I think he is a kind of opposition," he said. "He might leave."

I have not actually denied the replacement issue that has been raised in the meantime.

Matsui, a Marine General, has been an undisputed Defense Secretary to the Trump Administration, which has emphasized diplomatic solutions in the nuclear crisis last year.

It has been called the "axis of adults" with former Secretary of State Kelly White House and former Secretary of State Tylerson, serving as checks and balances in diplomatic and security policies.

It is said that President Trump has not been disconnected from his views because of his appearance, and that he was excluded from the discussion of key issues after the appointment of Pompei and Bolton as National Security Advisers earlier this year.

The New York Times reported last month that Mr. Trump could replace Mr. Mathis after the mid - November election, saying he hates him in the Democratic Party.

If Mathis is replaced, the effect on the North Korean nuclear negotiations will not be significant, but President Trump will have a stronger grip on the military policy on the Korean peninsula.