Story highlights First Lady Michelle Obama criticized Donald Trump's complaints about a microphone issue

She said individuals who are tweeting at 3 a.m. should not have their fingers on nuclear codes

(CNN) First lady Michelle Obama once again tore into Donald Trump while campaigning for Hillary Clinton, going after the Republican nominee for tweeting at 3 a.m. and for Trump's microphone issues at the first presidential debate.

"When it comes to the qualifications that we should demand of our president, to start with we need someone who will take the job seriously," Obama said in Charlotte, North Carolina -- the first of two campaign stops in the state Tuesday.

The first lady -- who never mentioned the Republican nominee by name -- also defended Clinton's stamina and toughness, which have been brought into question by Trump.

"When she gets knocked down, she doesn't complain, she doesn't cry foul," the first lady said while repeatedly tapping on her microphone in reference to Trump, claiming his debate microphone last week was "defective."

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