As if that button were not hot enough, he recently mused on a radio program that in response to a terrorist nuclear detonation in the United States, the American government ought to consider a retaliatory nuclear strike against Muslim holy sites.

Faced with outrage and demands for an apology from Muslim groups, Mr. Tancredo, who is no stranger to denunciations as a result of his position on immigration, has hung tough. He published an Op-Ed piece in the Denver Post on Sunday defending his comments. "Few can argue that our current approach to this war has deterred fundamentalists from killing Westerners ... That being the case, perhapsthecivilized world must intensify its approach. Does that meantheUnited States should retarget its entire arsenal on Mecca today? Does it mean we ought to be sendingStealth bombers on runs over Medina? Clearly not. But should we take any option or target off the table, regardless of the circumstances? Absolutely not, particularly if the mere discussion of an option or a target may dissuade a fundamentalist Muslim extremist from strapping on a bomb-filled backpack, or if it might encourage 'moderate' Muslims to do a better job cracking down on extremism in their ranks." Now, as it happens, I am opposed to nuking Mecca and Medina under any circumstances. The reason for that is that there would be no military justification for such an attack; its effect, in terms of human costs, would be entirely to kill civilians. Retaliation, by my moral reasoning, has to be directed at the actual perpetrators and those who harbor and enable them. The argument that Mecca is full of such enablers stretches the idea of culpability to the point at which it could justify the intended extirpation of Islam as such. The difference between "us" — among whom are many Muslims — and the jihadi terrorists is that "we" are not deliberate perpetrators of the slaughter of innocent people. "Our" moral worldview does not regard civilians as fair game.

But that does not exhaust the interest of Mr. Tancredo's statements, for two reasons. First, a not-inconsequential number of Americans probably agree with him, and who knows what polls would show following the nuclear destruction of an American city or two? Second, Mr. Tancredo, in his Op-Ed if not in his initial comments, couches his threat to Mecca in the name of deterrence: He wants to promise something so terrible to a would-be terrorist that the terrorist gives up his plans. This raises a slightly different question: Is it wrong to threaten to do something horrible in order to obtain a benefit from the threat? On the first point, many if not most Americans nowadays probably do harbor a post-tribal moral sensibility, according to which the deaths of non-Americans register as a loss that matters. This is classical liberalism overlain upon nationalist or tribalist sentiment, which it attenuates. For purposes of contrast, think of the proposition that "the only good Indian is a dead Indian" or the moral calculation that justified the firebombing of Dresden. American soldiers are dying in Iraq because of our liberality, our commitment to a decent government for Iraqis: Otherwise we could have flattened the place, turned the keys over to the toughest local goon, warned him to stay away from WMD, and left.

But the hold of this liberality over more primordial sentiments has not been tested by anything nearly as extreme as the death of scores of thousands of Americans in a nuclear terror attack. I hope it never is. But if it is, the authorities had better figure out a response that does justice to Americans' righteous anger. Otherwise they will likely be voted out in favor of someone promising more decisive action.

As for the deterrent value of Mr. Tancredo's threat, if I thought there was a significant wing of jihadi sentiment out there that A) might believe we'd do it; and B) would be so horrified at the thought as to abandon the quest for ways to kill us, then we would have crossed a threshold at which it would be worth having a discussion. But I don't. One important aspect of the problem we have is precisely that so many of these characters have not responded to deterrence theory.

Mr. Tancredo gets that. But he thinks the solution is to augment the threat. I don't think that will help, and I think it will only distract us from the task of identifying the bad guys and eliminating the threat they pose before they can act.