Joe Biden and Kamala Harris made an upbeat show of unity Thursday as they held their first joint public event since Harris replaced the president as the Democratic Party’s candidate in November’s election. Chants of “Thank you Joe!” rang out from the audience at a community college in the Maryland suburbs outside Washington. Biden announced a major deal to reduce medication prices for retirees on social welfare programs. But the biggest star was Biden’s vice president who has surprised many by uniting the Democratic Party and surging in the polls against Republican Donald Trump since her abrup…