They came from the Sierra Maestra mountains, led by a revolutionary of wild good looks and prodigious stamina, and promising a Caribbean Utopia in place of murderous gangster capitalism. Fidel Castro's guerrillas even promised democracy, but their leader swiftly harnessed communism to his personality cult instead. Half a century later, he has written a deluded 1,000-word resignation letter, published at midnight and prompting ritual tributes from his remaining friends on the wilder shores of Marxism. But the wider world should be under no illusion that he has wrecked his country. And the US, against which he defined it, should seize this moment to end a policy of non-negotiation that has failed utterly.

Admirers of Mr Castro's dictatorship hail as its crowning achievements an impressive health service, strong schools and universities and a clear sense of national identity. All three are indeed remarkable, compared with those of Haiti and perhaps the Dominican Republic. But Mr Castro's legacy is one of long-term economic collapse. An island rich in raw materials and with no shortage of trading partners despite a 45- year-old US embargo now produces less than half as much food as in 1959 and a tenth as much sugar. It is dependent on tourism for hard currency and Venezuela for oil, whose pledged aid in cash and kind exceeds in value that of the US to Israel.

Like Erich Honecker and other Eastern European leaders a generation ago, Mr Castro bequeaths to his successors misgovernment so endemic that, as one dissident put it recently, “prostitution, delinquency and corruption have become indispensable means of subsistence”. He also leaves a political system built around him and therefore condemned to instability without him; and an ideology whose clash with the US has reduced Cuba to irrelevance even at a regional level.

Yesterday President Bush said he hoped that Mr Castro's announcement would begin a transition to democracy, but indicated that serious US engagement would have to wait for “free and fair” elections. This is a policy drafted by Republicans in Washington but signed into law as the Helms-Burton Act by President Clinton after Cuban jets shot down two civilian US aircraft in 1996. Now more than ever, it is misguided.

Truly free elections are unlikely under any of Mr Castro's possible successors - but incremental reform, political as well as economic, is not. Raúl Castro, the outgoing leader's younger brother whom the US State Department has nicknamed “Castro Lite”, has in fact invited political debate on a limited but unprecedented scale since taking de facto power in 2006. He is likely to be installed formally as president this week. A likely first vice-president, Carlos Lage, was prevented only by the older Castro himself when he tried introducing a package of economic reforms in the early 1990s aimed at allowing small businesses to make a profit.

The obstacle-in-chief is leaving the stage at last. He says that he will fight on as “a soldier in the battle of ideas”, but that battle was lost decades ago, and most Cubans know it. Havana's youth have a clear sense of their isolation thanks to the internet, as Budapest's did in 1989 thanks to satellite TV. Across the Straits of Florida, Miami's younger Cuban exiles do not share the older generation's dogmatism; they just want to end the destitution of those they left behind. Mr Castro's departure, albeit to a peaceful retirement he scarcely deserves, is half the solution. US engagement is the other half. Its time has come.