Athletic. Amazing. Powerful. Phenomenal.

America's airwaves are jammed with superlatives to describe basketball star LeBron James, who began his first semifinal playoff series this week. No matter how Mr. James's Cleveland Cavaliers fare in their matchup against the Detroit Pistons, however, I've got my own description for his off-court decisions.

Cowardly.

James's teammate Ira Newble recently helped draft an open letter to the Chinese government, condemning its role in the ongoing genocide in Darfur. Everybody on the Cavaliers signed the letter except for James and Damon Jones. James said he didn't have enough information about the issue to take a stand. Mr. Jones wouldn't comment.

We can choose to take them at their word, of course – or we can follow the money. Jones has an endorsement contract with an up-and-coming Chinese shoe and apparel company. James has a $90 million deal with Nike, which has huge business interests in China.

And China has enormous interests in Sudan, where at least 200,000 people have been killed – and 2.5 million displaced – since 2003. Desperate to locate new energy sources, the Chinese invest a billion dollars a year in Sudan and purchase two-thirds of its oil. Proceeds from these sales help fund the Arab militia known as the janjaweed, which continues to murder, rape, and dismember non-Arabs in Sudan's western region of Darfur.

As Beijing prepares to host the 2008 Olympic Games, however, the Chinese have shown signs of softening their stance. Criticized by other Hollywood celebrities for serving as an artistic adviser to the Olympics, film director Steven Spielberg sent a letter in April urging China to help end "human suffering" in Sudan. Shortly thereafter, China dispatched an envoy to encourage the Sudanese government to accept a United Nations peacekeeping force in Darfur.

To be sure, China continues to block UN Security Council sanctions against Sudan. But the Spielberg episode suggests that the Chinese might be susceptible to more international pressure, especially if it threatens to mar their Olympic lovefest (slogan: "One World One Dream").

Mr. Newble knows all of that, of course, which is why his own letter explicitly links Darfur to the Olympics. "China cannot be a legitimate host to the [Olympics] ... while it remains complicit in the terrible suffering and destruction that continues to this day," Newble wrote.

Newble is hardly the first professional athlete to stick his neck out for a political cause. Tennis great Arthur Ashe denounced apartheid in South Africa; boxer Muhummad Ali resisted the draft during America's war in Vietnam, forsaking his heavyweight crown. But LeBron James, one of the best basketball players in the world, won't lift a finger for Darfur.

Here James echoes the dominant hoopster of his youth, Michael Jordan, who has a record of putting profits over principles. Mr. Jordan refused to endorse African-American Democrat Harvey Gantt in his bid to unseat Republican (and ex-segregationist) Jesse Helms in a racially tinged 1990 Senate race in Jordan's home state of North Carolina. "Republicans buy sneakers, too," he explained.

The Helms-Gantt election was, of course, a political contest. By comparison, the Darfur situation is an unconscionable crime against humanity. Politically speaking, it's a slamdunk. Every credible human rights organization has underscored the complicity of Sudan's government in the Darfur genocide; and even the Chinese acknowledge their support for this same government. As the 2008 Olympics get closer, the only question is what we're going to do about it.

Here you might object that the Olympics should be about sports, not politics. That's exactly what the Chinese have been saying, of course: just last week, China's foreign minister denounced Western activists for "trying to politicize the Olympic Games."

But the Games have always been political. They were political in 1936, when Adolf Hitler used the Berlin Olympics to burnish the Third Reich's international image; in 1968, when two African-American champions raised the black power salute as they received their medals; and in 1972, when terrorists abducted and killed 11 Israeli athletes.

The Games were political in 1976, when Taiwan walked out of the Olympics in Montreal to protest Canada's recognition of the People's Republic of China, and in 1980, when the United States and dozens of other nations (including China!) boycotted the Moscow Olympics in denunciation of the Soviet invasion of Afghanistan.

So the 2008 Olympics in Beijing will be political, too. Nobody knows that better than the Chinese government, which hopes the Games will showcase China as a modern, progressive society.

Ironically, LeBron James has not decided whether he will compete in Beijing. But in the real battle, over Darfur, James has elected to stay on the sidelines. That's his right, of course. And the rest of us have the right to call his behavior what it is.

• Jonathan Zimmerman teaches history and education at New York University.