CHARLOTTE—First Lady Michelle Obama never once mentioned Mitt Romney's name. But in her speech before the Democratic National Convention speech Monday night, she offered a dramatic contrast between her husband, Barack Obama, and his Republican opponent, insisting he understands the struggles of average Americans because he's lived through those tough times, too. "Barack knows the American Dream because he's lived it, and he wants everyone in this country to have that same opportunity, no matter who we are, or where we're from, or what we look like, or who we love," Michelle Obama said. "He believes that when you've worked...