Chances are that Monday’s tribute to Sen. Edward Kennedy at the Democratic National Convention will end with a clip of his pledge to the 1980 convention: “The work goes on, the cause endures, the hope still lives and the dream shall never die.”

For many, however, once the last Kennedy brother leaves the American political stage, the hope and the dream will live a little less vigorously.

“The dream will endure as a legacy to the Kennedys,” said Richard Reeves, the author of `President Kennedy: Profile of Power.’ But it is just that today, a dream. It’s not the reality of American politics.”

Kennedy is being treated for a malignant brain tumor, which means that this could be the last time that a Kennedy of his generation addresses a Democratic convention.

The 76-year-old Massachusetts Democrat taped a five-minute video message recently at his Cape Cod home to be shown at the Denver gathering. But, said Frank Mankiewicz, a top adviser to Robert Kennedy, “I have a feeling he could be there.”

Whether he appears or not, the hall will see and sense a coda to one of the enduring political sagas of the past half-century.

The family has been omnipresent in Democratic politics since John Kennedy’s insurgent vice-presidential bid electrified the 1956 convention. He lost, but the strength shown by the first-term, 39-year-old senator vaulted him to national prominence.

From that moment on, Kennedys provided eye-watering moments at Democratic conventions that few other American politicians could match, albeit moments that didn’t always benefit the larger Democratic cause.

Lyndon Johnson’s forces were said to be piqued in 1964 when, on the night of LBJ’s convention acceptance speech, delegates gave Robert Kennedy a 16-minute ovation before watching a film tribute to his slain brother.

Four years later, convention delegates stopped fighting each other over Vietnam long enough to watch “Robert Kennedy Remembered,” a Richard Burton-narrated Charles Guggenheim film about the assassinated senator. Delegates stood and cheered for five minutes, then sang “The Battle Hymn of the Republic.”

“The only moment of conciliation at that convention was the tribute to Bob,” recalled John Seigenthaler, a former aide to Robert Kennedy. The divided party nominated Vice President Hubert Humphrey and never really healed that year; Humphrey lost to Richard Nixon.

Even at the 1980 convention, though it was clear that Ted Kennedy had lost his bid to wrest the nomination from incumbent President Jimmy Carter, he dominated the proceedings. His forces led a bitter two-day platform fight that resulted in Kennedy getting the party to adopt his $12 billion recession-fighting plan. He also got a 40-minute ovation on the second night with his “dream will never die” speech. Carter lost the election to Ronald Reagan.

While the Kennedys kept a grip on the soul of the party, they often left the faithful with an image problem. They were derided by Republicans, comedians and party moderates as out-of-touch liberals, and the brothers were branded as playboys or worse.

“I don’t think many Republicans would want their kids to get in the car with Senator Kennedy,” said David Carney, former White House political director for President George H. W. Bush.

A 1969 incident shaped Ted Kennedy’s image for years. He drove his car off a bridge into the water on the Massachusetts island of Chappaquiddick. Passenger Mary Jo Kopechne, a 28-year-old campaign worker, was trapped in the car and drowned. Kennedy left the accident scene, waited hours before telling police and a week later went on national television to explain his actions.

He later pleaded guilty to leaving the scene of an accident after causing injury, and got a two-month suspended sentence.

After his 1980 White House bid, Ted Kennedy returned to the Senate and became known as a master of compromise, forging a reputation as a fighter for his causes. Universal health care, stronger educational standards, tax breaks for the less wealthy and unwavering support for labor became his hallmarks.

Sen. Barack Obama is in many ways the successor to those dreams. Ted Kennedy endorsed him early in the primary season, and Caroline Kennedy, President Kennedy’s daughter, is on Obama’s vice presidential selection team.

Still, the Democratic presidential candidate must tiptoe across a political tightrope. The Kennedys help him tap into an important, passionate political constituency, not to mention the money and expertise their network brings.

“There is a resonance with the Kennedys that motivates people to act on the basis of compassion,” Seigenthaler said.

But in some circles, the Kennedys remain political anachronisms, liberals long ago shorn of their charisma.

The evidence: Efforts by Kennedy children and relatives to win political races have languished, other than congressional seats with strong, sympathetic New England Democratic constituencies.

In 2002, Robert’s daughter Kathleen Kennedy Townsend became the first Democrat to lose a race for the governorship of Maryland in 36 years. In Massachusetts, Joe Kennedy, Robert’s son, has declined several times to run for governor; in 1997, he dropped his bid saying personal and family problems were hurting his candidacy.

Monday, the analysts say, Democrats must leave the audience remembering Ted Kennedy as not only the last lion of liberalism, but also a man whose hope will outlive him.

Reeves also said that once Ted Kennedy is gone, it’s inevitable that his convictions and compassion will lose their most ardent champion.

The Kennedys were, he said, “a continuation of a certain way of viewing government. They tried to keep breathing life into the New Deal. Ted Kennedy carries that on.

“The great senators stand for something, and they stay a long time and get things done. Ted Kennedy didn’t change.”