Massachusetts Senator Edward Kennedy, the liberal lion of the Democratic party, the hero of a dozen Democratic national conventions, took the stage at one more gathering of the faithful.

He delivered an endorsement that electrified the convention and held out the promise of a Democratic unity rooted in the heritage and mission of what many older Democrats still see as the party of the three young brothers: John, Bobby and Teddy.

Battling brain cancer in a fight for his life, Kennedy was earlier this summer not expected to be able to attend the convention that would nominate the man he supported for the presidency in the Democratic primaries: Barack Obama.

But in Denver, on Monday night, in front of a crowd of delegates, alternates and true-believing partisans that could not have cheered more loudly, Kennedy appeared.

To the chants of “Teddy! Teddy! Teddy!” the senator called the party to a place of communion and common faith not yet seen at a convention where supporters of two of Kennedy’s colleagues, Obama and New York Senator Hillary Clinton are still forging a sort of unity.

On Monday night, Obama and Clinton delegates cheered as one. They waved their signs with the name “Kennedy” and the blue-and-white colors of the senator’s 1980 campaign for the party’s presidential nomination. They cried together as the last of the Kennedy brothers declared that, “I come here tonight to stand with you to change America, to restore its future, to rise to our best ideals and to elect Barack Obama president of the United States.”

Telling Democrats why they are Democrats, as only this Kennedy can, the senator recalled that, “Together, we have known success and seen setbacks — victory and defeat — but we have never lost our belief that we are all called to (build) a better country and a newer world. And I pledge to you that I will be there on the floor of the United States Senate when we begin…”

Again came the cheers of “Teddy! Teddy! Teddy!”

Speaking of this moment as “a season of hope — new hope for a justice and prosperity for the many, not just the few,” Kennedy promised to join the fight once more for “the cause of my life”: “decent, quality health care as a fundamental right and not a privilege.”

“We can meet these challenges with Barack Obama,” Kennedy roared, echoing the slogan of the Illinois senator’s campaign. “Yes we can and, finally, yes we will.”

Comparing Obama with his presidential brother John, Ted Kennedy told the convention, “This November the torch will be passed again to a new generation of Americans.”

And, then, promising “not merely victory for our party but renewal for our nation,” Kennedy called the convention and the party to arms once more: “The work begins anew. The hope rises again. And the dream lives on.”

This convention is all about endorsements for Barack Obama.

They will be worded in many ways.

They will be spoken with varying levels of sincerity.

They will have different political meanings and potentials.

But none will touch so many delegates, so many Democrats, so many Americans as powerfully at that of the one man — the one last Kennedy — who really can speak of passing the torch that this party has followed for the better part of five decades.

UPDATE: Video of Kennedy’s speech below…