Sen. Ted Kennedy made gave a rousing speech at the Democratic National Convention tonight and did in about 10 minutes what it’s taken his party all summer to do: Give life to its general election message.

Kennedy is the heart of the liberalism that has defined the Democratic Party for 75 years. He’s referred to as the “lion” of the Senate—not only by virtue of the nine terms he’s spent in America’s highest lawmaking body, which make him the third-longest serving senator in the body, but also by virtue of his indefatigable determination, even in the face of a malignant brain tumor that has forced him into experimental treatment and has kept him out of the Senate for most of the past four months, to have a leading role in this history-making convention.

According to the talking heads narrating the event for us, convention organizers weren’t sure, even in the last few minutes leading up to the speech, whether Kennedy would be strong enough to deliver his remarks. CNN reported that Kennedy’s family had arranged for him to have a chair or stool of some sort available while he spoke.

As he did with the advice of his doctors who had advised him not to travel to Denver, he pushed it away.

On the heels of an emotional video tribute that recounted the service of and his relationship with his three older brothers—one of whom was killed in World War II, the other two of whom were assassinated before the world—Kennedy took the stage with all the vigor of a healthy man, determined to deliver a message that would bring the leaders of his party to their feet.

And he did.

Kennedy delivered a speech stamped with the Kennedy trademark, direct in its tone and heavy with the happy burdens of moral obligations that he believes Americans owe one another. But what was most remarkable about it, in the mind and eye of this humble blogger, was the reaction the party faithful had to it.

Here they have one of their longest-serving senators, the last living member of the generation of brothers that gave America two war heros, three United States senators, an attorney general and a president of the Unitest States. He is aged; he is ailing. Convention delegates knew, even as they watched an animated Kennedy fire away in vintage style, this is likely the last opportunity they’ll have as a party to thank him for his lifetime of service to their cause and their country.

For me, as a 31-year-old political observer who only has first-hand knowledge of one of those Kennedy brothers, it was almost surreal to watch. I have studied the lives of his brothers since even before I was an adult; the disquietude I felt, even as a 10-year-old, as I stood in Dealey Plaza was as deep then as it is unforgettable today. But there was something about watching Ted Kennedy tonight that, for the first time, made me feel that I had experienced some part of that famous Kennedy mystique.

Regardless of what you think of their politics (and virtually no one is tepid when it comes to their politics), the Kennedys are an American political institution. Their impact on this nation cannot be overstated. Their involvement in public service, in politics, in governance and in affecting change on so many issues throughout the last 50 years leaves a legacy that is unmatched in modern American history.

Kennedy used the final paragraph of his speech to signal a sea change in Democratic politics. Not only did he hand the leadership mantle of leadership of the party to Barack Obama and his generation, but in doing so, in the words of Republican strategist Alex Castellanos, he bypassed another American political family that at one time had seemed to be heir to that mantle: Bill and Hillary Clinton.

And Kennedy channeled his late brother, the president, as he did it:

This November, the torch will be passed again to a new generation of Americans. So, with Barack Obama and for you and for me, our country will be committed to his cause. The work begins anew. The hope rises again. And the dream lives on.

It was one of those moments for which conventions are still useful: The very weight of history unfolding before your eyes.

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