The epochal shock of the 9/11 attacks on America has waned over the 12-plus years since those airliners smashed any illusion of homeland invulnerability.

However, Thursday's moving dedication of the National September 11 Memorial Museum at - actually, under - Ground Zero in Lower Manhattan re-confirmed that this national resolve remains firm:

Terrorists will never defeat us.

Yes, al-Qaida zealots murdered nearly 3,000 people in New York City, northern Virginia and western Pennsylvania on Sept. 11, 2001.

But terrorists didn't - and can't - kill the American spirit.

Yes, we have serious divisions of opinion in our democratic republic, including an ongoing debate about how to counter the continuing threat of Islamic radical terrorism in the U.S. and around the world.

But President Barack Obama rightly stressed powerfully unifying themes while speaking at Thursday's ceremony in the new museum's Foundation Hall, which lies 70 feet below ground level amid twisted Twin Towers wreckage.

Addressing an audience that included family members of those killed on that terrible day, the president told the inspiring story of a young man who "emerged from the smoke, and over his nose and his mouth he wore a red handkerchief" while helping rescue people trapped in the chaotic inferno of the World Trade Center. "He led those survivors down the stairs to safety, and carried a woman on his shoulders down 17 flights. Then he went back. Back up all those flights. Then back down again, bringing more wounded to safety. Until that moment when the tower fell."

President Obama later added that the man's identity wasn't discovered until months later after his mother read a newspaper story about the brave one with the red bandana. She knew her son, who had died at age 24 in the Twin Towers, always carried a red handkerchief. Some survivors then confirmed that he was the man who had guided them out of harm's way.

His name was Welles Crowther. His mother, Alison Crowther, was there Thursday to hear the president say about him: "He worked in finance, but he had also been a volunteer firefighter. And after the planes hit, he put on that bandana and spent his final moments saving others."

The president also paid this stirring tribute to all of the 9/11 victims, its heroes and the Americans who have fought the good fight in their names:

"Here we tell their story, so that generations yet unborn will never forget. Of co-workers who led others to safety. Passengers who stormed a cockpit. Our men and women in uniform who rushed into an inferno. Our first responders who charged up those stairs. A generation of service members - our '9/11 Generation' - who have served with honor in more than a decade of war. A nation that stands tall and united and unafraid - because no act of terror can match the strength or the character of our country."

That strength and character, which were on such vivid display while our nation was under savage assault on Sept. 11, 2001, will endure.