The Martin Luther King Jr. Memorial on the National Mall in Washington, D.C., was supposed to be dedicated in August. But then Hurricane Irene paid a visit and the dedication had to be rescheduled. Thousands finally gathered for the ceremony Sunday, and the celebration included speeches by Rep. John Lewis and the Rev. Jesse Jackson, as well as a performance by Aretha Franklin. President Obama also spoke and called on Americans to do what needs to be done to face challenges in education, health care, and the economy. "Dr. King refused to accept what he called the 'isness' of today. He kept pushing for the 'oughtness' of tomorrow," Obama said. "Let us not be trapped by what is. We can't be discouraged by what is. We have to keep pushing for what ought to be." The guests then all joined in a singing of "We Shall Overcome."