After Benjamin Netanyahu's speech let me point you toward Jeffrey Goldberg's analysis. Let me also suggest, again, that differences on Iran policy correspond to answers to this one question: Whether the world of 2015 is fundamentally similar to, or different from, the world of 1938.

I've gone into the 1938 question before, here and here, but in light of the theme's centrality to this speech I'll do so one more time. No parallel from history is ever perfect, as Ernest May and Richard Neustadt so memorably argued in Thinking in Time. But as that book also demonstrated, the idea of recurring historic episodes has a powerful effect on decision-making in the here and now. Disagreements over policy often come down to the search for the right historic pattern to apply.

Over the years Benjamin Netanyahu has very explicitly said, "It's 1938 and Iran is Germany." For instance, see the the first minute of the clip below. Netanyahu said he was asked to give a young man a one-sentence summary of the world situation. Netanyahu answered with those six words.

In less explicit form, the idea that Europe on the eve of the Holocaust is the most useful guide to the world in 2015 runs through arguments about Iran policy. (Ted Cruz made the explicit comparison after the speech.) And if that is the correct model to apply, the right "picture in our heads" as Walter Lippmann put it in Public Opinion, then these conclusions naturally follow:

• The threatening power of the time—Nazi Germany then, the Islamists' Iran now—is a force of unalloyed evil whose very existence threatens decent life everywhere.

• That emerging power cannot be reasoned or bargained with but must ultimately be stopped and broken.

• "Compromisers" are in fact appeasers who are deluding themselves about these realities—Neville Chamberlain then, Barack Obama now—and increase danger for the world by wasting time before the inevitable showdown. The tellers of harsh truths—Winston Churchill then, Benjamin Netanyahu now—are trying to spare the world far greater dangers by encouraging action before it's too late.

1938, the first time around (Wikimedia)

• The appeasers' blindness endangers people all around the world but poses an especially intolerable threat to Jews. Six million of them were slaughtered because Britain, France, and especially the United States took too long to confront Hitler or even open their doors to refugees. Today's 8 million residents of Israel could be at existential risk if a mad regime, committed to their destruction, gains nuclear weapons. If a national leader says he intends to kill you, you take that seriously.

• As a result of all these factors, no deal with such an implacable enemy is preferable to an inevitably flawed and Munich-like false-hope deal.

That's what follows if the most relevant history is pre-Holocaust, pre-World War II Europe, and nearly everything in Netanyahu's speech can be read in this light. Also, and crucially, it means that the most obvious criticism of the speech—what's Netanyahu's plan for getting Iran to agree?—is irrelevant. What was the Allies' "plan" for getting Hitler to agree? The plan was to destroy his regime.

* * *

If, on the other hand, you think that the contrasts with 1938 are more striking than the similarities, you see things differently. As a brief reminder of the contrasts: The Germany of 1938 was much richer and more powerful than the Iran of today. Germany was rapidly expansionist; Iran, despite its terrorist work through proxies, has not been. The Nazi leaders had engulfed the world in war less than a decade after taking power. Iran's leaders, oppressive and destructive, have not shown similar suicidal recklessness. European Jews of 1938 were stateless, unarmed, and vulnerable. Modern Israel is a powerful, nuclear-armed force. Moreover, the world after the first wartime use of nuclear weapons, of course by the United States, is different from the world before that point. That is, all of humanity has faced an existential threat from nuclear warfare through the past 60 years. Eliminating the weapons is the only lasting protection; while they exist, deterrence has been the only way to keep them from being used.

So if it's not 1938, then other models of negotiation can apply, like those the United States used with the Soviet Union through the decades of the Cold War, or with China from the 1970s onward. Iran is then another problematic state, rather than a uniquely Nazi-style menace. (Recall that before the Iraq War Netanyahu made similarly absolutist claims about the undeterrable threat of Saddam Hussein.) Negotiations will therefore include, as they have with other states, a combination of carrots and sticks; a recognition of interests on all sides; and an understanding that negotiated progress is long, halting, and imperfect, but better than the alternative of no progress at all.

And if it's not 1938, analyses like this one, from the Arms Control Association after today's speech, have weight:

[Netanyahu] argues that the agreement-in-the-making would make it a near "certainty" that Iran pursues nuclear weapons because it would retain a nuclear program. This is just plain wrong.

The reality is that the agreement the P5+1 are pursuing would increase Iran's theoretical "breakout" time to amass enough enriched uranium gas enriched to bomb grade from today's 2-3 months to more than 12 months, and it would do so for over a decade. It would block the plutonium path to weapons.

* * *

Here's what I understand the more clearly after these past few weeks' drama over Prime Minister Netanyahu's speech. These differences in historic model are deep and powerful, and people with one model in mind are not going to convince people with the other mental picture. (Indeed after I rashly used the "is it 1938?" theme in a tweet, there was a little storm of responses in this vein: "@trueholygoat Serious question: Why do you hate Jews so much? ")

Unless Iran's behavior worsens in ways we have not yet seen, to me and others in the not-1938 crowd it will seem more comparable to other difficult states, for instance the old Soviet Union, than to Hitler's Germany. And unless its behavior improves in ways we have not yet seen, to Netanyahu and many others it will seem like the old threat in a new form, all the worse because of the nuclear element.

That is one more reality for negotiators to deal with. As Jeffrey Goldberg notes at the end of his post-speech report, Obama's task in trying to broker a deal is hard in the best of circumstances, and there's a reasonable chance that after this speech it has become harder.