Home In this screengrab taken from Twitter.com, former U.S. President Barack Obama endorses Democratic presidential candidate former Vice President Joe Biden during a video released on April 14, 2020. (Photo by Twitter via Getty Images) In this screengrab taken from Twitter.com, former U.S. President Barack Obama endorses Democratic presidential candidate former Vice President Joe Biden during a video released on April 14, 2020. (Photo by Twitter via Getty Images)

In this screengrab taken from Twitter.com, former U.S. President Barack Obama endorses Democratic presidential candidate former Vice President Joe Biden during a video released on April 14, 2020. (Photo by Twitter via Getty Images)

APRIL 14: In this screengrab taken from Twitter.com, former U.S. President Barack Obama endorses Democratic presidential candidate former Vice President Joe Biden during a video released on April 14, 2020. (Photo by Twitter via Getty Images)

U.S. President Barack Obama delivers remarks at a tribute to Vice-President Joe Biden (L) during an event in the State Dining room of the White House, January 12, 2017 in Washington, DC. (Photo by Olivier Douliery-Pool/Getty Images)