WASHINGTON (CNN) --
"Like all who have held this office before me, I have experienced setbacks," Bush said. "There are things I would do differently if given the chance. Yet I have always acted with the best interests of our country in mind.
"I have followed my conscience and done what I thought was right. You may not agree with some tough decisions I have made. But I hope you can agree that I was willing to make the tough decisions."
Bush also said he is "filled with gratitude," and characterized Obama's inauguration as a "moment of hope and pride for our whole nation."
"We have faced danger and trial and there is more ahead," Bush said. "But with the courage of our people and confidence in our ideals, this great nation will never tire, never falter and never fail."
He discussed the attacks of September 11, 2001, saying, "As the years passed, most Americans were able to return to life much as it had been before 9/11. But I never did.
"Every morning, I received a briefing on the threats to our nation. And I vowed to do everything in my power to keep us safe."
He noted "America has gone more than seven years without another terrorist attack on our soil."
However, the soon-to-be former president warned Americans that "our enemies are patient, and determined to strike again."
At the same time, "We must continue to engage the world with confidence and clear purpose. In the face of threats from abroad, it can be tempting to seek comfort by turning inward. But we must reject isolationism and its companion, protectionism."
The presidential farewell address is a tradition dating back to George Washington's departure from office in 1797. Presidents Eisenhower, Reagan, Carter and Clinton -- among others -- all delivered farewell speeches.
Bush leaves office with about one in four Americans approving of the job he is doing.
Bush is planning to spend the weekend at Camp David, Maryland, the presidential retreat, Perino said, before his term ends at noon Tuesday with the swearing-in of Barack Obama as the country's 44th president.