Eight years after Hillary Clinton set aside bad blood and a deflated ego to stump for the man who defeated her in the Democratic primary, President Obama will return the favor Tuesday. At a joint rally in Charlotte, North Carolina, the rivals-turned-partners will take the stage together in a bid to bring about Democratic unity and shore up support for one of the most unpopular major party presumptive nominees in history. To be sure, the event will include no small number of digs at the even more unpopular presumptive Republican nominee.