Our very beginnings defined us as a "can-do" people: We literally conceived a new nation, and then set out to conquer a continent.
We defined rights as individuals, but we worked together to raise a neighbor's barn, or to link a continent with rail.
We were oceans apart? Build a canal.
Did a mighty river plague us with floods and droughts? Dam it up with the biggest public works project in history. And that same Hoover Dam provided the power to the California defense plants that helped win a world war.
We were hungry for homes of our own? Build them by the millions in the suburbs, and link them to work with 60,000 miles of interstate highways.
Should our reach exceed our grasp? But the moon itself was in our grasp. And we led the way in making the world a click of the finger away.
And we were rich enough, powerful enough, to lead when disaster struck others: Herbert Hoover became a hero after the First World War by leading a massive relief effort in Europe.
After the Second World War, America sent everything from CARE packages to billions of dollars to put Europe's ravaged economies back on their feet.
The Berlin airlift of 1948 saved that beleaguered city; and Americans joined the Peace Corps decades later. And in the 21st century, this nation was half the world away when the tsunami struck Indonesia.
But when Katrina hit . . . nothing - not our wealth, our strength, our impulse to lend a hand - could prevent disaster. The experts warned this could happen; our leaders promised mobilization; and a major American city drowned.
Katrina, I think, was a portent that one of this country's most basic articles of faith was now in doubt. The failure to keep New Orleans from being overwhelmed by floodwaters was almost a precursor of our failure to keep our economy safe from near-collapse.
As much as any event in recent history, Katrina triggered a question we are still asking: "What has happened to our country?"