So, has the dream died?

Patrick Kennedy’s unexpected decision not to seek reelection to the US House prompted widespread reflection yesterday on how swiftly the political climate had changed, from the adulation for Edward M. Kennedy after his death to the voter fatigue that has helped end the family’s decades in power.

With Patrick Kennedy bowing out amid dismal poll numbers, some read the shift as a measure of the declining political cachet of the family name. Others say it goes deeper, reflecting the fading popularity of the activist federal government the Kennedy family has long championed.

“It is quite a landmark moment,’’ said Robert Dallek, a historian and biographer of John F. Kennedy. “It may be an indication that the Kennedy mystique and influence has run its course.’’

For some in Massachusetts, where the Kennedy family dominated public life for nearly seven decades, that was a shock.

“I think people felt there would always be a Kennedy in Congress someplace,’’ said Peter Meade, president and chief executive of the newly created Edward M. Kennedy Institute for the United States Senate in Dorchester.

“I think it’s a bit of a start for people to say, ’My gosh, there’s not one member of the Kennedy family in the federal government,’ ’’ Meade said. “It gives people pause.’’

It was just over five months ago that the death of Patrick Kennedy’s father prompted an extraordinary outpouring of affection for his life and legacy, as tens of thousands of mourners lined roads from Hyannis Port to Boston to salute his passing hearse and world leaders filled a church in Mission Hill for his funeral Mass.

Then his nephew Joseph P. Kennedy II decided not to run for his seat, paving the way for an obscure Republican state senator named Scott Brown to ride his pickup truck to victory over the candidate the Kennedys ultimately backed, Democrat Martha Coakley. Brown even campaigned on a pledge to stop a Democratic plan to overhaul health care, which Edward Kennedy had called “the cause of my life.’’

The fading fortunes of the Kennedy family seemed to reflect the changing political landscape that has imperiled President Obama’s agenda in Washington, Dallek said.

“Symbolically,’’ he said, “it may speak to this shift away from an interest in federal activism in pursuit of social reforms.’’

When Patrick Kennedy clears out his Capitol Hill office after eight terms, it will draw the curtain on a 64-year period during which at least one Kennedy was either in the White House, the US House, or the US Senate.