There are two images from the night my friend Barack Obama was elected president of the United States that stand out for me.

The first is of America’s beautiful new first family striding onto the stage in Chicago’s Grant Park surrounded by a sea of jubilant supporters — some dancing, some hugging, many in tears. That image was recorded by hundreds of news cameras and beamed around the world.

The other image was captured by just one photographer. Fifteen minutes before the president-elect was to begin his acceptance speech, the photographer grabbed his camera and raced to the Lincoln Memorial.

He expected to find a crowd, he wrote in The New York Times. “Instead, I found 25 or so people who had made their way in the dark to the marble steps of the memorial and stood silently around a lone transistor radio.” On the spot where Dr. Martin Luther King Jr. delivered his “I Have a Dream” speech, under the watchful gaze of Abraham Lincoln, “they listened, some crying in the drizzle, as Barack Obama began his address before the Grant Park multitude.”

It was no accident that those 25 or so people found their way to the Lincoln Memorial on election night. And it was no coincidence that President-elect Obama and Vice President-elect Biden celebrated their arrival in Washington this past weekend with a gala concert at that memorial.

Our Founders declared that we are all endowed with an inalienable right to liberty, but they could not reconcile their noble ideals with the ignoble practice of slavery. It required an Abraham Lincoln to give fuller meaning to our national creed of “liberty and justice for all.”

A century later, speaking at the foot of the Lincoln Memorial, Dr. King spoke of his dream of an America where we are judged on the content of our character and not the color of our skin. It was that America that elected Barack Obama president.

We are proud in Illinois to call our state the Land of Lincoln. But on Nov. 4, all of America became the Land of Lincoln.

This week — when we also celebrated the 80th birthday of Dr. King and prepare to celebrate the 200th birthday of Abraham Lincoln — we can all take pride in what this election represents. As President-elect Obama said in his remarks at Grant Park, “If anyone out there still doubts that America is a place where all things are possible; who still wonders if the dream of our Founders is alive in our time; who still questions the power of our democracy,” this election is your answer.

We have not yet reached the mountaintop that Dr. King spoke of. But with this historic new administration, we have reached a new summit.

Beyond the celebrations of this past weekend lay some of the most serious challenges our nation has ever confronted: the gravest financial crisis in nearly a century, an urgent energy and climate challenge, two wars, a deadly and determined enemy, and increasing turmoil in some of our world’s most troubled places.

We have made genuine progress on race. But the challenge of unequal justice is not limited to race.

We no longer condone the overt racism of Jim Crow and “whites only” drinking fountains. But many still excuse and justify discrimination and unequal justice based on such distinctions as national origin and sexual orientation.

As we confront these and other challenges, we would be wise to remember the great and enduring lesson of Abraham Lincoln: America’s greatest strength is in our unity. We should remember, as our new president reminds us, that we are — and always will be — the United States of America.

On election night, when that photographer arrived at the Lincoln Memorial, he found one TV crew near the Reflecting Pool. They appeared to be waiting for a crowd to arrive. Seeing the photographer’s camera, one of the crew members said, “Nothing to see here.”

How wrong he was.

What you see in that election night photo at the Lincoln Memorial is America’s long struggle to make real the dreams of our Founders. You see our enduring, deep and passionate longing to be one nation, one people, undivided.

That is one of the images I will think about as my friend Barack Obama takes the oath of office as America’s 44th president.