When it started, American teenagers were doing "The Twist." The United States had yet to put a man into orbit around the Earth. And a first-class U.S. postage stamp cost 4 cents.

The world is much changed since the early days of 1962, but one thing has remained constant: The U.S. economic embargo on communist-run Cuba, a near-total trade ban that turned 50 on Tuesday.

Supporters say it is a justified measure against a repressive government that has never stopped being a thorn in Washington's side. Critics call it a failed policy that has hurt ordinary Cubans instead of the government.

All acknowledge that it has not accomplished its core mission of toppling Fidel and Raul Castro.

"All this time has gone by, and yet we keep it in place," said Wayne Smith, who was a young U.S. diplomat in Havana in 1961 when relations were severed and who returned as the chief American diplomat after they were partially re-established under President Jimmy Carter.

"We talk to the Russians, we talk to the Chinese, we have normal relations even with Vietnam. We trade with all of them," Smith said. "So why not with Cuba?"

In the White House, the first sign of the looming embargo came when President John F. Kennedy told his press secretary to go buy him as many H. Upmann Cuban cigars as he could find. The aide came back with 1,200 stogies.

Kennedy announced the embargo on Feb. 3, 1962, citing "the subversive offensive of Sino-Soviet communism with which the government of Cuba is publicly aligned."

It went into effect four days later at the height of the Cold War, a year removed from the failed CIA-backed Bay of Pigs invasion meant to oust communism from Cuba and eight months before Soviet attempts to put nuclear missiles on the island brought the two superpowers to the brink of war.

Washington already had some limited sanctions in place, but Kennedy's decision was the beginning of a comprehensive ban on U.S. trade with the island that has remained more or less intact ever since.

Little was planned to mark Tuesday's anniversary, but Cuban-American members of Congress issued a joint statement vowing to keep the heat on Cuba.

Supporters of the policy acknowledge that many U.S. strategic concerns from the 1960s have been consigned to the dustbin of history, such as halting the spread of Soviet influence and keeping Fidel Castro from exporting revolution throughout Latin America. But they say other justifications remain, such as the confiscation of U.S. property in Cuba and the need to press for greater political and personal freedoms on the island.

"We have a hemispheric commitment to freedom and democracy and respect for human rights," said Jose Cardenas, a former National Security Council staffer on Cuba under President George W. Bush. "I still think that those are worthy aspirations."

With just 90 miles (145 kilometers) of sea between Florida and Cuba, the United States would be a natural No. 1 trade partner and source of tourism. But the embargo chokes off most commerce, and the threat of stiff fines keeps most Americans from sunbathing in balmy resorts like Cayo Coco.

Cuba is free to trade with other nations, but the U.S. threatens sanctions against foreign companies that don't abide by its restrictions. A stark example arrived off the coast of Havana last month: A massive oil exploration rig built with less than 10 percent U.S. parts to qualify under the embargo was brought all the way from Singapore at great expense, while comparable platforms sat idle in U.S. waters just across the Gulf of Mexico.

The embargo is a constant talking point for island authorities, who blame it for shortages of everything from medical equipment to the concrete needed to complete an eight-lane highway spanning the length of the island. Cuba frequently fulminates against the "blockade" at the United Nations and demands the U.S. end its "genocidal" policy.

Every fall, like clockwork, the vast majority of nations agree, and overwhelmingly back a resolution condemning the embargo. In November, 186 countries supported the measure, with only Israel joining the U.S. in opposition.

Also each year, Cuba updates its estimate of how much the embargo has cost it, using a complicated — and some say flawed — calculus that takes into account years of interest, the end of the gold standard and other factors. Last year's estimate summing 49 years of sanctions was $975 billion.

Even some critics of the embargo call Havana's claims exaggerated, saying that while the sanctions had a tremendous impact when first put in place, Cuba was able to adapt and benefited from relationships with like-minded allies such as the former Soviet Union and Venezuela.

"There's no doubt that the embargo is detrimental to the Cuban economy. It complicates international financial transactions, but more importantly, it limits Cuban families' access to medicine," said Geoff Thale, a Cuba analyst at the Washington Office on Latin America, which supports ending the policy. "At the same time, Cuba's economic problems go beyond the embargo."

While 50 years of socialism have brought advancements in areas such as education and health care, even island authorities acknowledge their perennially struggling economic system must change. President Raul Castro is in the process of allowing more private-sector activity, decentralizing state-run businesses, implementing agricultural reform and slimming government payrolls.

The United States actually does have significant trade with Cuba under a clause allowing the sale of food products and some pharmaceuticals.

According to the most recent information available from Cuba's National Statistics Office, the U.S. was the island's seventh-largest trading partner in 2010, selling $410 million in mostly food products. However, that was down from nearly $1 billion in 2008, as the island increasingly turned to other countries that don't force it to pay cash up front.

Many U.S. businesses would love to be allowed into the Cuban market, but an end to the embargo seems a long way off.

The issue is seen as a political nonstarter in the United States, where every four years, presidential candidates take turns courting the Cuban-American vote in Florida, a key swing state.

President Barack Obama has said Raul Castro's economic openings are insufficient, and it's unlikely he would do anything in an election year to risk losing support in Florida, which he won in 2008. Even if he wanted to lift the embargo, the Helms-Burton Act of 1996 stipulates that it would have to be approved by Congress.

Raul Castro, for his part, says recent changes in the U.S. such as allowing Cuban-Americans to visit relatives more often and send them more money are merely cosmetic.

Backers of the sanctions say it's as important as ever to maintain what they call the moral high ground, saying islanders will be grateful whenever change does come.

Critics cite the annual U.N. votes to argue that times have changed and the embargo is a Cold War relic that ought to be thrown onto the scrap heap.

"It's no longer a matter of the United States leading a movement to isolate Cuba in the hemisphere," said Smith, a staunch opponent of the embargo. "Quite the contrary: If anyone's isolated, on this issue anyway, it's us."

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