In a highly political dedication speech as he girds for a bruising reelection battle, Obama launched a thinly-veiled verbal attack on Republicans and today's Washington gridlock. In the same address, he urged supporters to be patient in their yearning for change, which he promised he would deliver. "As tough as times may be, I know we will overcome," he declared, standing under the new 30-foot granite monument to the civil rights legend. "I know there are better days ahead. I know this because of the man towering over us. Obama paid tribute to King's "moral imagination" and invoked the bitter struggle of the slain civil rights hero, while portraying today's villains as those resisting efforts to progress and create a fairer society. "As was true 50 years ago, as has been true throughout human history, those with power and privilege will often decry any call for change as divisive. They'll say any challenge to the existing arrangements are unwise and destabilizing," he said. With anti-capitalist protesters capturing the imagination of an America crippled by stubbornly high 9.1 percent unemployment, Obama said King would not have looked for scapegoats. "If he were alive today, I believe he would remind us that the unemployed worker can rightly challenge the excesses of Wall Street without demonizing all who work there," he said. After the address, Obama held hands with wife Michelle and Vice President Joe Biden to sing the civil rights anthem "We shall overcome," swaying with a crowd of thousands at the new memorial unveiled on the National Mall. The event had the atmosphere of a political rally as speaker after speaker before Obama linked King's memory to today's intractable politics, with Democrats and Republicans so divided over the size and scope of government. "When met with hardship, when confronting disappointment, Dr. King refused to accept what he called the is-ness of today," the president said. "Let us not be trapped by what is. We can't be discouraged by what is. We've got to keep pushing for what ought to be, the America we ought to leave to our children, mindful that the hardships we face are nothing compared to those Doctor King and his fellow marchers faced 50 years ago." Tens of thousands of predominantly African Americans descended on Washington for the dedication ceremony to honor the man whose "I Have a Dream" speech helped galvanize a movement in the 1960s. US civil rights leader Reverend Jesse Jackson, who was a friend and colleague of King's, called him a "living force" even today, decades after his death, with poverty and privation still rampant in the United States. "I see him as a living force and the day when I think about more wars, more concentrations of wealth, more poverty and then more rebellion, Dr King would be in the middle of the struggle today," Jackson said. "Dr King would make a case for we must measure our character by the way we treat those on the hull of the ship, not just those on the deck of the ship." Hurricane Irene's passage through the eastern United States had prompted the postponement of the ceremony on August 28, which was the 48th anniversary of the "I Have a Dream" speech in Washington. The King monument, the only one on the Washington Mall not dedicated to a US president or to war, had already been open to the public for weeks. Dedicated to the 1964 Nobel Peace Prize laureate and his message of democracy, hope, justice and love, the memorial has been installed on a vast open space of four acres (1.5 hectares) dotted with cherry trees donated by Japan. Nearby is the Lincoln Memorial from where the pastor gave his most famous speech on August 28, 1963. A massive, 28-foot (nearly nine-meter) "Stone of Hope" statue in the likeness of King, carved out of white granite by renowned Chinese sculptor Lei Yixin, shows him gazing sternly out onto the horizon, arms folded. Visitors enter through the Mountain of Despair, a huge boulder symbolizing the African American struggle for peace and equality. Since King's time, most Americans say there has been progress toward his dream, but that a gulf still exists between blacks and whites. A recent USA Today poll found 90 percent of whites and 85 percent of blacks believe civil rights for blacks have improved in their lifetime, although whites are more likely to see the progress as far-reaching. The poll showed 54 percent of blacks and 49 percent of whites said the dream of racial equality had been achieved.