Joe Biden is facing growing calls to select a Black woman as his running mate as an acknowledgement of their critical role in the Democratic Party and a response to the nationwide protests against racism and inequality. The shifting dynamics were clear late Thursday when Amy Klobuchar took herself out of contention for the vice presidency. Biden, the presumptive Democratic presidential nominee, has already pledged to select a woman as his vice president to energize the party’s base with the prospect of making history.