WASHINGTON — For nearly five decades, the United States has pursued a policy toward Cuba that could be described as incredibly stupid.

It could also be called childish, irresponsible and counterproductive — and, since the demise of the Soviet Union, even insane. Absent the threat of communist expansionism, the refusal by successive American presidents to engage with Cuba has not even a fig leaf’s worth of rationale to cover its naked illogic. Other than providing Fidel Castro with a convenient antagonist to help him whip up nationalist fervor on the island — and thus prolong his rule — the U.S. trade embargo and other sanctions have accomplished precisely nothing.

Now, with Fidel ailing and his brother Raul acting large and in charge, the United States has its best opportunity in years to influence the course of events on the island. George W. Bush, as one might have expected, won’t do the right thing. It will be up to the next president.

Raul Castro is 76, just five years younger than his more charismatic brother, and since assuming the presidency he has acted as if he knows he doesn’t have much time to waste. In short order, he has repealed restrictions that prohibited Cubans from buying personal computers, cell phones and other consumer goods — items that Fidel feared might facilitate sedition or, at a minimum, promote counterrevolutionary comfort and lassitude.

It’s true that these measures are largely symbolic — on an average salary of about $17 a month, most Cubans can’t dream of buying a computer, and in any event the Cuban government still strictly controls access to the Internet. Likewise, any Cuban who owns a cell phone can’t use it without paying the astronomical rates demanded by Cubacel, the government cell-phone monopoly.

But at the same time, Raul has encouraged the first stirrings of debate in the government-controlled media (which are the only media) — something Fidel never would have allowed. Rumors that the government will soon permit widespread private ownership of automobiles, and perhaps even allow an aboveboard private market in real estate, seem much less implausible than they would have just six months ago.

I’ve been to Cuba as a journalist 10 times, and friends on the island — including some harsh critics of the Castro regime — say that there is real optimism about the prospects for change.

Bush’s response has been a cold shoulder. In remarks a few days ago, the president did little but state the obvious fact that Raul Castro is not, and never will be, a believer in democracy. He dismissed the recent measures as “empty gestures at reform,” and then proceeded to make an empty gesture of his own: He said he would change U.S. policy to allow Cuban-Americans to send cell phones to their relatives on the island, which is something many families already have done.

Raul Castro is not going to transform Cuba into a free-market democracy. But he gives every indication of moving at least some distance down the path that China’s leadership has taken, toward becoming a free-market, one-party autocracy. That’s certainly not a perfect outcome, as shown by recent events in Tibet. But it’s impossible to deny that the Chinese people enjoy far greater personal freedom than they did, say, 20 years ago. Why wouldn’t Washington want to encourage Havana to become more like Beijing?

That would require actual engagement with the Cuban government, though, and Bush doesn’t intend to allow anything of the sort.

On Friday, Barack Obama appeared before the Cuban American National Foundation — one of the most powerful and most strident of the Miami-based anti-Castro groups — and said that if he were elected president he would conduct “direct diplomacy” with Cuba’s leadership. Earlier in the week, John McCain spoke to an audience in Miami and essentially vowed to continue Bush’s hard-line course.

Obama’s into-the-lion’s-den performance may win him some points for bravery, but may not get him a lot of votes in south Florida. He has the right idea, however. The United States can attempt to influence any changes that eventually take place in Cuba, or it can harrumph from the sidelines. Several of Cuba’s leading dissidents have urged the White House to end the decades-old trade embargo and the draconian restrictions on travel to the island. Bush pays no attention to those on the front lines of this struggle.

Stubbornly sticking with a policy that has achieved nothing in nearly 50 years is a pretty good definition of insanity.

Eugene Robinson’s e-mail address is eugenerobinson(at)washpost.com.