"When making life-or-death, war-or-peace decisions, a president just cannot pop off or lash out irrationally. No, we need an adult in the White House, I guarantee you," she said at an election rally in support of Hillary Clinton in Philadelphia as she made a strong pitch for the 68-year-old Democratic presidential candidate.
Michelle, without mentioning Trump, 70, said the US needs someone who is compassionate.
"Someone who will be a role model for our kids. Someone who is not just in this for themselves but for the good of this entire country - all of us. At the end of the day, the presidency does not change who you are, it reveals who you are and the same is true of a presidential campaign," she said.
"So if a candidate is erratic and threatening; if a candidate traffics in prejudice, fears and lies on the campaign trail; if a candidate thinks that not paying taxes makes you smart, or that it is good business when people lose their homes; if a candidate regularly and flippantly makes cruel and insulting comments about women, about how we look, how we act - well, sadly, that is who that candidate really is. That is the kind of president they will be," she said.
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"Because the minute that individual takes that oath, they are under the hottest, harshest light there is, and there is no way to hide who they really are. But see, at that point, it is too late. They are the leader of the world's largest economy, Commander-in-Chief of the most powerful military force on Earth. With every word they utter, they can start wars, crash markets, fundamentally change the course of this planet," she warned.
Michelle said Clinton is the best one to be the next president of the US.
Michelle said for those who question Clinton's stamina to
be president, her resilience is more than proven.
Clinton is the only candidate in this race who has travelled to 112 countries; who has negotiated a ceasefire, a peace agreement, a release of dissidents; who has spent 11 hours testifying before a congressional committee, she said.
"Hillary is one of the few people on this entire planet - and clearly the only person in this race - who actually has any idea what this job entails, who has seen it from every angle - the staggering stakes, the brutal hours, the overwhelming stresses. And here is the thing - she still wants to do this job because she believes that she has an obligation to use her talents. What do we teach you all? To use your talents to help as many people as possible. That is why Hillary Clinton is running," Michelle said.
"I am inspired by her lifelong record of public service. No one in our lifetime has ever had as much experience and exposure to the presidency - not Barack (Obama), not Bill (Clinton), nobody - and, yes, she happens to be a woman," she added.