All's fair in politics. John McCain and Sarah Palin have every right to bring up William Ayers, even if his connection to Obama is minor, even if Ayers's Weather Underground history dates back to Obama's childhood, even if establishment Republicans and Democrats alike have collaborated with the present-day Ayers in educational reform. But it's not just the old Joe McCarthyesque guilt-by-association game, however spurious, that's going on here. Don't for an instant believe the many mindlessly "even-handed" journalists who keep saying that the McCain campaign's use of Ayers is the moral or political equivalent of the Obama campaign's hammering on Charles Keating.

What makes them different, and what has pumped up the Weimar-like rage at McCain-Palin rallies, is the violent escalation in rhetoric, especially (though not exclusively) by Palin. Obama "launched his political career in the living room of a domestic terrorist." He is "palling around with terrorists" (note the plural noun). Obama is "not a man who sees America the way you and I see America." Wielding a wildly out-of-context Obama quote, Palin slurs him as an enemy of American troops.

By the time McCain asks the crowd "Who is the real Barack Obama?" it's no surprise that someone cries out "Terrorist!" The rhetorical conflation of Obama with terrorism is complete. It is stoked further by the repeated invocation of Obama's middle name by surrogates introducing McCain and Palin at these rallies. This sleight of hand at once synchronizes with the poisonous Obama-is-a-Muslim e-mail blasts and shifts the brand of terrorism from Ayers's Vietnam-era variety to the radical Islamic threats of today.

That's a far cry from simply accusing Obama of being a guilty-by-association radical leftist. Obama is being branded as a potential killer and an accessory to past attempts at murder. "Barack Obama's friend tried to kill my family" was how a McCain press release last week packaged the remembrance of a Weather Underground incident from 1970 — when Obama was 8.

We all know what punishment fits the crime of murder, or even potential murder, if the security of post-9/11 America is at stake. We all know how self-appointed "patriotic" martyrs always justify taking the law into their own hands.

Obama can hardly be held accountable for Ayers's behavior 40 years ago, but at least McCain and Palin can try to take some responsibility for the behavior of their own supporters in 2008. What's troubling here is not only the candidates' loose inflammatory talk but also their refusal to step in promptly and strongly when someone responds to it with bloodthirsty threats in a crowded arena. Joe Biden had it exactly right when he expressed concern last week that "a leading American politician who might be vice president of the United States would not just stop midsentence and turn and condemn that." To stay silent is to pour gas on the fires.