Jonah seems upset that when I complain that American conservatives are perpetuating a "stab in the back" theory of the war in Iraq to explain away their own hideous errors of strategic judgment without bothering "to make a tight link between the National Socialist reaction to German surrender at the end of WWI." Kevin Baker's already lay it out [sic] in Harper's at some length, so I haven't bothered personally...
Suffice it to say that I think the main point of analogy is that mainstream contemporary American conservatism, like inter-war Nazism, believes that military defeats are primarily due to failures of national will. They believe this in part because they massively overestimate the significance of will in determining outcomes of this sort. They also, like Nazis, seem to deny that it might ever better serve the national interest to abandon a military adventure than to continue it. These beliefs serve to foster the further belief that several constitutive elements of liberal democracies -- committed to free speech, to unfettered political debate, the existence of active political opposition movements -- are a source of national weakness.
I've written at great length here and on Spinsanity about attacks on dissent since 9/11, so I share Matt's concern about the increasing volume of rhetoric that attempts to blame opponents of the war for "betraying" US troops and causing defeat in Iraq.
With that said, however, the comparison to Nazis is not helpful. As I wrote in a discussion with Yglesias a couple of years ago, these analogies are almost never appropriate. First, they're obviously overrepresented in contemporary debate because they are highly accessible in people's minds and can be used to smear the other side with negative associations (as in Godwin's law). And even when Nazi analogies are being used with serious intent, they still are likely to (a) automatically bring to mind negative associations between the other side and Nazis and (b) turn the debate into a foodfight.
To illustrate the way this works, note that Yglesias refers exclusively to "interwar Nazism" and "Nazis" in the post above. However, as Baker recounts, the phrase "stabbed in the back" was first coined by Paul von Hindenburg, a German general in WWI who served as president of the Weimar Republic and not a Nazi (though he eventually capitulated to Hitler and appointed him Chancellor in 1933). And the idea that "military defeats are primarily due to failures of national will" and that "several constitutive elements of liberal democracies ... are a source of national weakness" are (sadly) hardly unique to Nazis.