By Elinor Shields
Fidel Castro's Cuba has endured a US embargo for decades
The departure of Fidel Castro from power has long been a goal of US policy, but Washington reacted warily to the news it had been working for for nearly 50 years.
Reports that the leader who has outlasted nine US presidents had temporarily handed over to his brother for health reasons offered no prospect for an end to the stand-off between the two states, officials said.
"The fact that you have an autocrat handing power off to his brother does not mark an end to autocracy," White House spokesman Tony Snow said.
US President George W Bush, meanwhile, has urged Cubans to work for democratic change.
But as Mr Castro's ill-health fuels public speculation on the island's future, the US is privately weighing its plans for a possible new era in Cuba.
Beyond the Castros
For decades the US has been labouring to end Cuba's communist government - through the failed 1961 Bay of Pigs invasion, assassination attempts, diplomatic isolation and the economic embargo imposed in 1962.
The Bush administration has stepped up efforts to hasten a transition to democratic rule, through tighter enforcement of the embargo and the creation of a multi-agency Commission for Assistance to Free Cuba.
In its first report in 2004, the group outlined the steps the US was prepared to take to bring about regime change, such as the subversion of Mr Castro's plans to hand over power to his younger brother Raul.
A follow-up report last month recommended an $80m fund to support Cuba's opposition and the deployment of US aid once a transitional government was in place.
And last year, US Secretary of State Condoleezza Rice announced the creation of a new post to help "accelerate the demise" of the Castro government.
"We will continue to offer support for a real transition," Cuba Transition Co-ordinator Caleb McCarry told the New Yorker magazine before Mr Castro's health problems became known.
But some analysts say the US policy had failed to advance national or Cuban interests - and Washington should now engage with the island.
"In the end [Castro's demise] is a Cuban problem," Nicholas Robins, a visiting scholar at Duke University's Center for Latin American and Caribbean Studies, told the BBC.
"It is not an American problem, nor should it be."
But many in South Florida's Cuban-American community disagree - and have set out to make the island's fate an "American problem".
The fate of Elian Gonzalez was a flashpoint in US-Cuban relations
This week has seen thousands in Miami celebrating what they see as the demise of the Cuban leader, in the latest display of hostility to a man many of them deem a tyrant.
Such attitudes - and influence - also drove the 2000 saga surrounding Elian Gonzalez, the five-year-old Cuban shipwreck survivor who became the symbol of a bitter dispute between two nations and one family.
The exile leadership launched the Cuban American National Foundation (Canf), which led the drive to found US-funded television and radio broadcasts into Cuba.
They are a "defining and pervasive influence on US policy," Mr Robins said.
A possible new era in Cuba also brings questions and concerns for Washington.
The US fears that social instability after Mr Castro's death could provoke a huge wave of emigration.
Washington is worried by Venezuela's ties with Cuba
Washington has called for Cubans on both sides of the Florida Straits to stay put.
"It would cause a tremendous loss of life, plus be a disorderly thing that at this moment in history the United States just cannot tolerate," said Senator Mel Martinez, a Florida Republican who was born in Cuba.
Another US fear is that Mr Castro's allies in the region, such as Venezuela's President Hugo Chavez, might intervene to influence a transition.
''The president is worried about people in the neighbourhood who seek to destabilise neighbours using economic or other means,'' Mr Snow said.
For now though, Washington is waiting amid the uncertainty.