On Jan. 20, 1993, I entered the Oval Office for the first time as president. As is the tradition, waiting for me was a note from my predecessor, George Herbert Walker Bush. It read:

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Dear Bill,

When I walked into this office just now I felt the same sense of wonder and respect that I felt four years ago. I know you will feel that, too.

I wish you great happiness here. I never felt the loneliness some Presidents have described.

There will be very tough times, made even more difficult by criticism you may not think is fair. I'm not a very good one to give advice; but just don't let the critics discourage you or push you off course.

You will be our President when you read this note. I wish you well. I wish your family well.

Your success now is our country's success. I am rooting hard for you.

Good Luck - George

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No words of mine or others can better reveal the heart of who he was than those he wrote himself. He was an honorable, gracious and decent man who believed in the United States, our Constitution, our institutions and our shared future. And he believed in his duty to defend and strengthen them, in victory and defeat. He also had a natural humanity, always hoping with all his heart that others' journeys would include some of the joy that his family, his service and his adventures gave him.

His friendship has been one of the great gifts of my life. From Indonesia to Houston, from the Katrina-ravaged Gulf Coast to Kennebunkport - where just a few months ago we shared our last visit, as he was surrounded by his family but clearly missing Barbara - I cherished every opportunity I had to learn and laugh with him. I just loved him.

Many people were surprised at our relationship, considering we were once political adversaries. Despite our considerable differences, I had admired many of his accomplishments as president, especially his foreign policy decisions in managing America's response to the end of the Cold War and his willingness to work with governors of both parties to establish national education goals. Even more important, though he could be tough in a political fight, he was in it for the right reasons: People always came before politics, patriotism before partisanship. To the end, we knew we would never agree on everything, and we agreed that was OK. Honest debate strengthens democracy.

While we maintained a respectful, friendly relationship throughout my presidency, it was only when President George W. Bush asked us to jointly spearhead American relief efforts in the wake of the Indian Ocean tsunami of 2004 and again after Hurricane Katrina in 2005 that we got to really know each other. When we met with children who lost their parents in the tsunami, he was moved almost to tears when they gave us drawings they'd made to capture their pain and slow recovery in grief counseling. When we were asked to speak together at Tulane's graduation in 2006, I saw his genuine feeling for the students, many of whom had suffered in the flooding of New Orleans, and others who had shown heroism and love in caring for their neighbors. "Each of you here has inspired me," he told them. "When I look at our world, the good I see far outweighs the bad, which maybe explains why I am a real optimist about the future that you all will be facing."

Growing old did not rob him of his optimism or his love of competition and adventure. In his book of letters, there's a wonderful one to his family about getting older, in which he crows about driving his speedboat off the Maine coast. "Still want to compete. I still drive Fidelity II fast - very fast. My best so far - 63 mph in a slight chop with one [Secret Service] agent on board." I took more than one ride in that boat with him over the years. It was fun but not an experience for the faint of heart. It was the same driving spirit, coupled with heartfelt patriotism, which led him to volunteer for the Navy on his 18th birthday instead of attending Yale, becoming one of the youngest American pilots to get his wings. Even when he was later shot out of the sky, the sole survivor of his close-knit crew, he never feared to go up again - famously learning to skydive at 75.

After the war, he took a leap of faith by staking his and his family's future in the Texas oil business and eventually got into politics. Fifty years ago this spring, as a congressman representing Houston, he voted for the Fair Housing Act of 1968, going against his nearly perfect record of conservative votes in Washington. When he returned to Houston, he held a town hall to explain his vote to a hostile crowd who thought he'd lost his mind. He believed that he could convince them it was the right thing to do, as long as they would hear him out. That evening, at least, he was right. When he was finished talking he got a standing ovation.

Given what politics looks like in America and around the world today, it's easy to sigh and say George H.W. Bush belonged to an era that is gone and never coming back - where our opponents are not our enemies, where we are open to different ideas and changing our minds, where facts matter and where our devotion to our children's future leads to honest compromise and shared progress. I know what he would say: "Nonsense. It's your duty to get that America back."

We should all give thanks for George H.W. Bush's long, good life and honor it by searching, as he always did, for the most American way forward.

Former Republican President George H.W. Bush, left, and former President Bill Clinton, visiting Bush, pose for a photo with Sully, a yellow Labrador retriever who'll be Bush's first service dog at his home in Kennebunkport, Maine, Monday, June 25, 2018. The 94-year-old and his new companion got acquainted Monday at the Bush family compound on the coast of Maine. (Evan F. Sisley/Office of George Bush via AP)

Bill Clinton is the 42nd president of the United States.