Celebrated author and poet Maya Angelou on Wednesday cited Martin Luther King Jr. and the poll tests of the Jim Crow South in asking President Obama's supporters to vote this year.

Angelou, a longtime Obama supporter who was awarded the Presidential Medal of Freedom at a 2011 White House ceremony, wrote in an email sent through the president’s reelection campaign:

“My grandmother and my uncle experienced circumstances that would break your heart. When they went to vote, they were asked impossible questions like, ‘How many angels can dance on the head of a pin?’ When they couldn't answer, they couldn't vote.”

She also recalled that she had once discussed with King whether the United States would ever have an African-American president. She said that King predicted it would take about 40 years, whereas she had contended it would not happen in her lifetime.

“I have never been happier to have been proven wrong,” she noted.

The email is a reminder of the carefully targeted voter appeals that both presidential campaigns have made this year. Although Angelou’s email was not sent only to African-Americans — and its first sentence began “I am not writing to you as a black voter” — the memories she cited clearly have special resonance in the black community.

Obama received the support of 95 percent of African-American voters against Sen. John McCainJohn Sidney McCainMcConnell: 'Whoever gets to 60 wins' on immigration Meghan McCain: Melania is 'my favorite Trump, by far' Kelly says Trump not likely to extend DACA deadline MORE in 2008, amid historically high black voter turnout. His campaign is striving to limit any drop-off in enthusiasm this year.

Angelou’s email included a link to a tool on the Obama campaign website that enables supporters to remind friends to vote.