By KAT STAFFORD Associated Press DETROIT (AP) — Joe Biden's Democratic presidential campaign has launched a new national ad focused on Black Americans, urging them to stand up to President Donald Trump the way their ancestors stood up to 'violent racists of a generation ago.' The one-minute ad, which was shared exclusively with The Associated Press before its digital and television release on Thursday, is meant to drum up support among Black Americans, a key constituency for Biden, ahead of November's general election. The ad, titled 'Better America,' also takes a direct swipe at Trump, without mentioning the Republican president […]