In 2009, Ruslan Tsarni and his nephew Tamerlan Tsarnaev had a bitter argument over the implications of their faith. Tsarnaev announced he had chosen "God's business" over work or school. "I was shocked when I heard his words, his phrases, when every other word he starts sticking in words of God," says Tsarni. "There is someone who brainwashed him, some new convert to Islam." The falling out ended their relationship.
This was more than a family disagreement. It is a debate being conducted, in various forms, in Egypt, Nigeria, Indonesia, the Caucasus, the Palestinian territories and other places. Over the last several decades, traditional forms of Islam have been challenged by radical variants, which often latch onto ethnic and tribal resentments. Disaffected, angry young men can be particularly receptive, causing turmoil in families, mosques, regions and countries.
In our country, such radicalism is rare -- a tribute to America's special superpower of assimilation -- but not unknown. And it seems particularly difficult for us to account for. As the circumstances surrounding the Boston bombings have clarified, some of the reactions have been ideologically reflexive and counterproductive.
Portions of the left turned to any artifice -- including an attack on "white privilege" -- to avoid a serious discussion of radicalism and terrorism. Even the use of the word "terrorism" is viewed as a threat to multiculturalism or the prelude to a new round of civil rights abuses in the war on terrorism.
But the threat of terrorism is real, whether a given ideology finds it convenient or not. Consistent pressure on terrorist networks, including drone strikes, has made spectacular, al-Qaida-like attacks less likely. Yet homegrown, jihadist-inspired violence is a continuing danger. A number of attacks -- including in Times Square and on the New York subway -- have been prevented. Until the one in Boston that wasn't. It was the arrival of a long-held fear: decentralized violence against "soft" targets -- as soft as the spectators at a sporting event.
When suspected of radicalism, Tamerlan Tsarnaev was hardly subject to abusive or oppressive treatment. If anything, his case raises the question of what it would take -- in addition to the warning of a foreign government, defiance during an FBI interview and international travel to a terrorism-prone region -- to trigger heightened scrutiny.
Yes, the Boston bombing is an isolated case, but one that proves an isolated case can cause a million people to shelter in place. And one reason it doesn't happen more often is that an extensive apparatus of homeland security -- designed, equipped and trained over the last decade -- helps keep it from happening.
But elements of the right suffer their own form of ideological impairment. Their tendency is to regard terrorism and Islam as interchangeable. During the Boston manhunt, Rush Limbaugh predicted that the politically correct media would "circle the wagons" and say that "this is not because of Islam."
Yet some things, rather than being politically correct, are just correct. The Boston bombing was not because of Islam, as most Muslims understand it. Islam is a diverse religious tradition including more than 1 billion people and millions of our fellow citizens who overwhelmingly reject the murder of random strangers as an expression of their faith. Terrorism is the expression of a violent ideology that has, disturbingly, taken root among some Muslims.
Debates over the meaning of terms such as "jihad" and "Shariah" are at least as complex as Christian debates over "just war" and "social justice." For an outsider to assert that Islam should be generally identified with its most radical theological and political interpretation is both presumptuous and uninformed. When considering the religious argument between Ruslan and Tamerlan, why should conservatives assume that Tamerlan's interpretation of Islam was the more authentic?
This working assumption is entirely unworkable for anyone charged with leadership. While it is hard to even imagine such reckless folly, consider an American president who, following a terrorist attack, said, "This is because of Islam." He would alienate an entire faith tradition from the American experiment. He would insult every Muslim ally and Muslim soldier who fights at our side against terrorism. He would fulfill the fondest hope of Islamist radicals: to turn the war against terrorism into a civilizational conflict between the West and Islam.
Somehow, Americans of every ideological background need to be able to hold two ideas in their heads at once. The threat of terrorism is lethal and ongoing. But a war on Islam would make a war on terrorism impossible.
Email Michael Gerson of The Washington Post at email@example.com.