"The reason so many of us can't move forward is because we're cramped in a space too small to hold our spirit," Winfrey told attendees at the museum's inaugural Women's E-3 Summit on Empowerment, Entrepreneurship, and Engagement. "You have to be in alignment with what it is you want to do."She called on attendees to "dream bigger, be better, and allow ourselves to move around fearlessly."Winfrey toured the exhibit — titled "Watching Oprah: The Oprah Winfrey Show and American Culture" — on Wednesday. During her keynote Thursday, she also recited Sojourner Truth's now famous 1851 speech, "Ain't I a Woman?""This question is at the heart of black women's experience," she said. "It's been difficult for us to be heard, but not anymore, because we have the National Museum of African American History. I'm here to tell you that its very creation, its very existence, it being here screams 'hear me, hear me now.'"The talk show host, actress and philanthropist sparked buzz about a potential presidency with her rousing Cecil B. DeMille Award acceptance speech during the Golden Globes. However, she has repeatedly ruled out a presidential run. In an interview with CNN's Van Jones on "The Van Jones Show" in March, Winfrey said the bid for the presidency wasn't for her. However, she said "the noise about running for president moved me so humbly and deeply."President Donald Trump in March mocked Winfrey publicly at a campaign rally, telling the crowd she was the person he'd most like to run against in 2020 because he knows "her weakness" and predicting that a presidential campaign "would be a painful experience for her."The National Museum of African American History's Oprah exhibit opens Friday and runs through June 2019.