Sen. Ed Markey Edward (Ed) John MarkeyMassachusetts town clerk resigns after delays to primary vote count Bogeymen of the far left deserve a place in any Biden administration Senate Democrats urge Amazon to recall, stop sales of explosive products MORE (D-Mass.) said on Tuesday that President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE's claim that the U.S. nuclear launch button is "much bigger" than North Korea's "borders on presidential malpractice."

"Imagine being a servicemember or the family of a servicemember stationed in Korea and reading this," Markey tweeted. "This borders on presidential malpractice."

Imagine being a servicemember or the family of a servicemember stationed in Korea and reading this. This borders on presidential malpractice. https://t.co/rII95iu0Vm — Ed Markey (@SenMarkey) January 2, 2018

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Markey's tweet followed one by Trump, in which the president warned that the U.S. nuclear launch button was "more powerful" than the one North Korean leader Kim Jong Un claimed to have in a New Year's Day speech this week.

In that speech, Kim said that the world would have to accept North Korea as a nuclear-armed state, saying the fact that he had a nuclear launch button on his desk was a "reality," as opposed to a threat.

Trump's tweet appeared to challenge that claim. He also warned that the U.S. launch button actually worked.

Trump and North Korea have exchanged barbs for much of his first year in office, as Pyongyang stepped up the pace of its intercontinental ballistic missile tests.

The U.S. president has also repeatedly warned that possible military action against North Korea remains on the table if deemed necessary.