On my most recent visit to Cuba this past March, I brought my family with me, because I wanted my children to see what Cuba looked like before everything changed. I didn't realize quite how quickly that change would come.

In Havana, we stayed on the Plaza de Armas, a square that is in the heart of the old city, a carefully restored neighborhood in a capital that is otherwise collapsing on itself. Each morning, booksellers would set up stands in the square, and each morning, my 13-year-old son would roam about, talking to the booksellers and taking pictures of their shelves. One morning, he rushed back to the hotel to report on a fascinating conversation. One of the booksellers had asked him, "What do you think of Communism?"

We had briefed the children on the nature of totalitarian societies, and on the need to be discreet in public commentating—especially since I was in Cuba as a journalist, and especially since the government had shown interest in my movements. "What did you say?" I asked. He answered: "I said, 'I think it's interesting,' and then he said, 'Well, I think it's bullshit.'''

It is easy to understand why a bookseller on the Plaza de Armas would think this way: Censorship laws, and custom, and the secret police, guarantee that the only books sold on the square are mildewed Chomskys and Che hagiographies.

There will be many ways to test whether the Obama administration, and those who support its decision to reestablish ties with Cuba after a half-century hiatus (including yours truly), are correct in arguing that broad exposure to America, to its people and to its businesses, will translate into greater openness and freedom for ordinary Cubans. One of the most important ways to measure this will be to watch levels of Internet connectivity—open, affordable, unfiltered connectivity. Many Cubans I've met have quite literally never been on the Internet. In two years, if rates of exposure to the Internet remain the same, then the great Obama experiment could be judged, provisionally, a failure.

Critics of Obama's overture to Cuba argue that close U.S. ties with Vietnam and China are proof that exposure to America does not translate into political freedom—it translates into greater access to Coca-Cola products, but not to the spread of American ideals of free speech and pluralism. These critics have a point, of course (though critics of these critics also have a point: If the U.S. can have normal diplomatic and commercial ties with China, a terrible violator of human rights, why should it not have normal diplomatic and commercial ties with Cuba, a country ruled by a government that is less malignant than China's?).

Cuba, of course, is not China, and it is not Vietnam: China is large enough to create its own weather, and Vietnam is 8,000 miles away. The U.S. will have influence in Havana—a 45-minute flight from Miami—in profound and useful ways (and also potentially negative ways: I know, as a patriotic American, that I'm supposed to argue for the uncomplicated benefits of unfettered capitalism, but I would say that the Plaza de Armas will not necessarily be improved by the presence of a Burger King).

Here is my modest Plaza de Armas test: If, in two years, the booksellers on the plaza are selling books about something other than Che, and if they're making actual money selling more of what they want to sell, then the argument that engagement leads to openness will look credible. I'm not expecting anything close to perfect freedom—I'd be surprised, in two years, to find Marco Rubio's memoir for sale on the plaza—but I'll go looking for some proof that change is actually happening. Internet connectivity, the release of political prisoners, the establishment of non-government newspapers—these are bigger tests. But the plaza test will be telling nonetheless.