By Stephen Sackur BBC Washington correspondent

His grin was more dazzling than the tropical Cuban sun.

Jimmy Carter was in his element last week as he led the press, his entourage and a phalanx of Cuban secret servicemen on a sweaty tour of Communism's last redoubt.

From Washington... there were no words of praise for Mr Carter's courageous and creative diplomacy

Jimmy Carter may not have been much of a president but he is undoubtedly one of the best ex-presidents America has ever had.

Dignified, with his silver hair and courtly manner, and deeply committed to peace, democracy and conflict resolution, Mr Carter saw his visit to Cuba as an opportunity to break down years of hostility and paranoia.

The high point, indeed the most dramatic political moment Cubans have witnessed in decades, came with the former president's address to the Cuban nation.

With Fidel glowering into his beard just yards away, Mr Carter spoke for 20 minutes in laboured Spanish.

Winning Cuban hearts

His words were broadcast, uncensored and live, on local television.

"Cubans deserve the freedom to change laws peacefully by direct vote," said Mr Carter.

"After 43 years of animosity we hope that you can reach across the divide and join the community of democracies.

Carter's speech made history in Castro's Cuba

"And I hope the American people will open their arms and welcome you as friends."

Stirring stuff and revelatory for a Cuban audience long used to a fawning, party-controlled political culture dominated by the overwhelming presence of Comandante Castro.

But Mr Carter's speech was also directed at an audience on the other side of the Florida Straits.

America's punitive economic embargo on Cuba should be lifted, he said, and Americans should be allowed to travel freely to Cuba.

"I want the people of the US and Cuba to share more than a love of wonderful music and baseball," he went on. "I want us to be friends and respect each other."

Twenty-four hours later, Cubans showed the world what they thought of that sentiment.

As Mr Carter prepared to throw the first pitch in a specially arranged baseball game in Havana's creaking national stadium, tens of thousands of fans roared their approval.

Double standards

From Washington, however, there were no words of praise for Mr Carter's courageous and creative diplomacy.

I don't like to see someone appearing as a tourist and enjoying himself in a place where I know people are rotting in dungeons

Bush official

Instead, the Bush team delivered a verbal slap to the former occupant of the White House.

One administration apparatchik managed rather successfully, if unconsciously, to sum up the tone of sneering self-righteousness that pervades current US policy on Cuba.

"I don't like to see someone appearing as a tourist and enjoying himself in a place where I know people are rotting in dungeons," he said.

It is worth pausing for a moment to appreciate the breathtaking hypocrisy.

Only a few months ago, George Bush himself was taking snapshots of the Great Wall of China during a visit to the People's Republic.

When I last checked, China was holding thousands of political prisoners.

That did not stop the US president cosying up to the Beijing leadership and supporting their entry into the World Trade Organization.

Demonising Cuba

But now it is not just Cuba's human rights record that is under fire from Washington.

In a pre-emptive broadside fired at Havana just before Jimmy Carter's visit, John Bolton, undersecretary of state for arms control, accused Fidel Castro of developing a biological weapons capability.

Cuba, it seems, is close to becoming a paid-up member of the "Axis of Evil".

Quite an achievement for a Caribbean island of 11 million with a tottering economy barely kept afloat by sugar cane and tourist dollars.

Fidel, of course, made an extravagant meal of the American accusations.

A three-hour anti-imperialist rant on Cuban television was followed by a choreographed visit to one of Cuba's bio-tech research stations.

Jimmy Carter and the rest of us were treated to slides and graphs illustrating just how successful Cuba's civilian vaccination programme has been.

Yes, there are links with Iran, Libya and others, the comandante acknowledged, but the goal is saving lives not spreading weaponised germs.

That will not wash with George W Bush.

In a world of good guys and evil-doers, Cuba's pariah status is guaranteed.

Which is convenient for the Bush family at this particular time because being tough on Castro pays political dividends in Florida, with its influential community of anti-Castro Cuban exiles.

Florida stakes

It just so happens that Jeb Bush is running for re-election as governor of the Sunshine State this autumn.

It would be disastrous for Jeb if his big brother made any conciliatory gesture towards Havana.

Florida's Cuban exiles are key voters for both president and governor

And George W has his own re-election prospects to think about too.

He all but lost Florida last time and cannot afford to lose it next time.

Which means every effort will be made to keep the anti-Castro legions happy.

If that sounds cynical, it is.

That is what a week considering US-Cuba relations does to you.

Consider the case of Kevin Allen, a 56-year-old American who went to Cuba recently to scatter the ashes of his parents outside the Cuban mission church they had helped to build many years ago.

Mr Allen was fined $7,500 for flouting the ban on US travel.

A 75-year-old grandmother, Marilyn Meister, was similarly punished for taking a cycling holiday on the island.

Both were prosecuted under the terms of the Trading with the Enemy Act.

Far from easing these ludicrous restrictions, President Bush wants them enforced more rigorously.

Cuba is still a very convenient enemy.