The popular First lady said, "A President can not just pop off, or lash out irrationally ...we need an adult in the White House."

She said that "The presidency does not change whop you are, it reveals who you are."

Without naming Republican presidential nominee Donald Trump she said. "If a candidate is erratic and threatening, if a candidate traffics in prejudice fear 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."

She argued the case for Clinton saying she is "tough" citing her record as First Lady of Arkansas, First Lady of the United States, Senator from New York and Secretary of State adding "and yes, she happens to be a woman."

She added, "Being president isn't anything like reality TV, it is not an apprenticeship, and it is not just about fiery speeches or insulting tweets, its about whether someone can handle the awesome responsibility leading this country."

Michelle Obama has proven to be an especially powerful advocate for Clinton, her husband's one-time rival. Her speech in support of Clinton at the Democratic convention in July was praised as one of the best of that event.