Michelle Obama has been called the president’s secret weapon. On Monday night, she was Hillary Clinton ’s.

Until the first lady took the stage, the Democratic National Convention’s opening night mostly had been defined by episodic jeering from supporters of the presumptive Democratic presidential nominee’s primary foe, Sen. Bernie Sanders, I-Vt. But Obama’s passionate endorsement of Clinton and jabs at Republican nominee Donald Trump were met with thunderous applause.

Following an opening hour during which Clinton and Sanders delegates interrupted speaker after speaker by shouting each other down, Obama showed why many political strategists believe she will be a campaign-trail force as Clinton seeks to rally her base and attract independent voters in key swing states.

Obama began speaking about her daughters and the lessons they drew from watching campaigns.

“In this election, and every election, is about who will have the power to shape our children for the next four to eight years of our lives,” Obama said. “And I am here tonight because in this election there is … only one person who I think is qualified to be president. And that is our friend Hillary Clinton.”