Shugaban Amurka Barack Obama da Mataimakinsa Joe Biden, sun yi jawabi a rana ta uku a babban taron Democrat da ake yi a Philadelphia, inda Biden ya jinjina ma na gaba da shi, Shugaba Barack Obama, ya kuma jaddada cancantar 'yar takarar jam'iyyarsu a zaben shugaban kasar na 2016, Hillary Clinton.