On Tuesday, as people from all walks of life come together in common purpose to begin the work of renewing America's promise, my daughters and I will stand beside my husband as he takes the oath of office as the 44th president of the United States.

People have asked me how I'll feel at that moment. As a wife, I'll be thinking about how proud I am of my husband and how I believe so deeply that he will be an extraordinary president. As a mother, I'll be bursting with pride at the thought of my girls now being able to envision endless choices for themselves and the joy it will be to watch them grow up in the White House. And as a daughter, I'll be profoundly grateful to my parents, knowing that I am here only because of their lifetime of faith and hard work.

They're my proof that the American promise endures. It's that promise we all share — that our children might grow up with unlimited possibility, that our families might know the dreams of opportunity and prosperity, that people in every nation might look at the proud banner of this country and know the boundless meaning of hope.

As I take on my newest role — First Lady — I'll be thinking about what that promise means to all those whom I've had the humbling privilege to meet these past two years on the campaign trail: Americans across the country who opened their doors and hearts to share their stories with me — stories I carry to this day.

I particularly cherished my visits with military families all across the country. I met so many strong and inspiring military spouses eager to share their stories, their dreams for the future and the unique challenges they face because of their families' selfless service to our country.

And if there's one thing I learned, it's that when our servicemen and women go to war, their families go with them. I saw how they take care of each other, heard how they fill in whenever the system fails and discovered that the trials they faced always were matched by the hope they shared that better days are still ahead.

The simple 35-word oath my husband will take and the peaceful transfer of power it completes makes it easy to forget that the great fortune of our citizenship isn't free at all. It's a responsibility inherited only because generations of Americans have fought and bled and died for it.

So as I watch Barack take that oath, I'll be thinking especially about those members of our American family who stand guard across the world and the loved ones who await their safe return. Because even as we mark this moment in American history, there still will be empty seats at the dinner table; there still will be spouses struggling to juggle roles and responsibilities; there still will be children who mark the passing of a birthday without Mommy and toddlers who know their father only by a grainy video stream from a far-flung corner of the globe.

My husband and I are deeply grateful for the sacrifices that these families make to protect all American families. And we join them — today and every day — in praying for their loved ones and their safety. They don't ask a lot in return, just a Washington that understands the challenges they face as part of their extraordinary commitment to our country.

My husband understands that commitment, and he will ensure America lives up to its end. As military families join us on Tuesday, in person and in spirit, I want each and every one of them to know that for as long as I have the tremendous honor of being your First Lady, your voices will be heard, you will have an advocate in the White House, and the American promise you preserve always will extend to you, too.

All of us can learn a fundamental lesson from our military families: You don't need to wear a uniform to serve your country. We all have something to contribute to the life of this nation.

Monday is Martin Luther King Jr. Day. And to honor the legacy of a man who believed that everybody could be great because anybody can serve, my family and I will spend the day performing activities in service to others. And we'll ask all Americans to join us in making an ongoing commitment to serve their community and their country, because in this new season of hope, that's the only way we'll begin renewing America's promise for all who reach for it and all who defend it — as one nation and one people.

On Tuesday night, my husband and I will tuck in our daughters like we always do. Their bedrooms will be different, their home unfamiliar. But they will drift off to sleep protected by that same sacrifice that has kept all of our families safe and safeguarded our freedom for generations — the sacrifice of our men and women in uniform and their families.

For that, we could not be more grateful — or more proud.

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