KEY POINTS:
The news that Edward Kennedy, the patriarch of America's most famous political dynasty, has a malignant brain tumour will shock Americans.
Democrats and Republicans alike see him as a living link to a less divisive, more optimistic America.
Public admiration for the rumpled and avuncular
Boston politician has been unstinting.
The youngest of four Kennedy brothers, he has lived a life marked by relentless tragedies n his oldest brother, Joe, was killed in the Second World War, personal triumphs, a string of highly publicised personal failings and a spirit of optimism and joie de vivre.
During his four decades in politics, Mr Kennedy has used the bully pulpit of the US Senate, with his unmistakable Boston twang, and the clout of his name to give unstinting support for the cause of equal opportunity to the poor, to immigrants, and above all to children.
In the race for this year's Democratic nomination, Mr Kennedy provided a much needed boost of credibility to the campaign of Barack Obama, when the Democratic establishment was tilting towards Hillary Clinton.
His endorsement could not stop Mr Obama from losing Massachusetts, but it symbolised a handing over of the Kennedy torch to the insurgent candidate at a crucial moment.
The second most senior Democrat in the Senate, Mr Kennedy has been the leading liberal voice in US politics for decades.
He is the youngest brother of the late President John F Kennedy, shot dead in 1963, and of Robert Kennedy, assassinated five years later.
Mr Kennedy made an abortive run for the presidency in 1980, but forged his career in the US Senate where he has served since 1962.
In 2006, Time magazine named Mr Kennedy one of "America's 10 Best Senators", saying he had "a titanic record of legislation affecting the lives of virtually every man, woman and child in the country".
His brain tumour was discovered after the 76-year-old senator for Massachusetts suffered a seizure last weekend.
Tests revealed a tumour in the left parietal lobe of his brain. He is expected to undergo an aggressive combination of radiation and chemotherapy.
Mr Kennedy had a seizure at the family's compound in Cape Cod on Saturday and was airlifted to Massachusetts General Hospital in Boston, where his family have remained with him each day.
His prognosis remains unclear but the average period of survival ranges from less than a year for the most aggressive types of brain cancer to about five years for slower-growing tumours.
The tributes to Mr Kennedy have been generous.
The Republican presidential candidate, John McCain, rushed out a statement wishing a man he described as one of his closest friends in the Senate well. Another decades-long conservative friend of Mr Kennedy's called Fox News to sing the praises of Mr Kennedy's private and public kindnesses.
The caller described Mr Kennedy's career of caring for the poor and how he made time to serve food to the homeless.
President George Bush was the beneficiary of Mr Kennedy's willingness to put principle ahead of partisan politics. Almost alone among Democrats, he supported some of Mr Bush's educational reforms.
Mr Bush has phoned the senator in hospital to wish him well.
- THE INDEPENDENT