By ZEKE MILLER, JONATHAN J. COOPER, AAMER MADHANI and DARLENE SUPERVILLE CHICAGO — Former President Barack Obama, Michelle Obama and second gentleman Doug Emhoff will speak Tuesday on the second day of the Democratic National Convention, turning the party’s attention toward Vice President Kamala Harris and her faceoff against Republican Donald Trump. The pivot toward the presidential campaign’s final 76 days follows an opening night that was designed to give a graceful exit to the incumbent president, who was greeted with a hero’s welcome for stepping aside for Harris. Speaking clearly and energetically, Biden appeared to relish the chance to defend his record, advocate for his vice president and assail Trump.