For many years, a quiz titled "Al Gore or the Unabomber?" circulated on conservative websites.
The quiz juxtaposed passages from the former vice president's eco-manifesto "Earth in the Balance" with quotes from Theodore Kaczynski's critiques of industrial civilization and asked the reader to guess which writer was which.
Was it the bearded hermit who hailed "isolated pockets of resistance fighters" for struggling against modern society's "assault on the earth"? No, that would be the former vice president.
Was it Kaczynski, the mathematics Ph.D. turned mad bomber, who complained about the "destructive" impact of bringing a child into "the hugely consumptionist way of life so common in the industrial world"? No, Gore again.
Enterprising left-wing bloggers have already begun to play a similar game with Anders Behring Breivik, the Norwegian man who apparently justified last week's mass murder of helpless teenage campers with a 1,500-page "compendium" calling for a right-wing revolution against Europe's ruling class.
Judging by the manifesto's contents, Breivik has roughly the same relationship to the cultural right that Kaczynski had to certain strains of environmentalism. The darkest aspects of his ideology belong strictly to the neo-fascist fringe.
But many of his beliefs and arguments echo the rhetoric of mainstream cultural conservatives, in Europe and America alike.
Despite what the Norwegian authorities suggested over the weekend, those beliefs probably aren't a form of Christian fundamentalism. Breivik's writings bear no resemblance to the theology of a Jerry Falwell or an Oral Roberts, and his nominal Christianity ("I guess I'm not an excessively religious man," he writes at one point) seems to be more of an expression of European identity politics and anti-Islamic chauvinism than any genuine religious fervor.
But it's fair to call Breivik a right-winger. As Commentary Magazine Editor John Podhoretz put it, the Norwegian killer is "exactly the kind of psychotic ideologue of the right so many in this country instantly assumed Jared Loughner, the schizophrenic who shot Rep. Gabrielle Giffords" to be.
His compendium quotes repeatedly from conservative writers on both sides of the Atlantic, and it's filled with attacks on familiar right-wing targets: Secularism and political correctness; the EU and the sexual revolution; radical Islam and the academic left.
Indeed, stripped of their context, some of his critiques of multiculturalism and immigration resemble arguments that have been advanced, not just by Europe's far-right parties, but by mainstream conservative leaders such as David Cameron in Britain, Angela Merkel in Germany and Nicolas Sarkozy in France.
This means that last week's tragedy is also a political opportunity for Europe's left-of-center politicians, should they choose to respond to Breivik's rampage the way President Bill Clinton responded to the 1995 Oklahoma City bombing.
Timothy McVeigh's connections to Republican politics were several degrees short of tangential, but Clinton successfully linked the heartland terrorist to talk radio and the government shutdown, implying that McVeigh's crime was part of a broader story of antigovernment conservatism run amok.
Judging by Breivik's manifesto, the Continent's left-wing parties won't have to work nearly that hard to connect the Norwegian's act of terrorism to Europe's broader rightward turn.
How should European conservatives react? Not with the pretense that there's somehow no connection whatsoever between Breivik's extremism and the broader continental right. While his crimes should be denounced and disowned, their ideological pedigree has to be admitted.
But this doesn't mean that conservatives need to surrender their convictions. On the big picture, Europe's cultural conservatives are right: Mass immigration really has left the Continent more divided than enriched, Islam and liberal democracy have not yet proved natural bedfellows and the dream of a postnational, postpatriotic EU governed by a benevolent ruling elite looks more like a folly every day.
Extremists only grow stronger when a political system pretends that problems don't exist.
Conservatives on both sides of the Atlantic have an obligation to acknowledge that Anders Behring Breivik is a distinctively right-wing kind of monster. But they also have an obligation to the realities that this monster's terrible atrocity threatens to obscure.
Ross Douthat's column is distributed by the New York Times News Service.