CHICAGO (AP) — Warning of a difficult fight ahead, former President Barack Obama and Michelle Obama have called on the nation to embrace Kamala Harris in urgent messages to the Democratic National Convention that were at times both hopeful and ominous. “America, hope is making a comeback,” the former first lady declared. She then tore into Republican Donald Trump, a sharp shift from the 2016 convention speech in which she told her party, “When they go low, we go high.” Barack Obama, the first Black president in U.S. history, insisted the nation is ready to elect Harris, who is of Jamaican and Indian heritage and would be the nation’s first female president.