As far as nationalizing things, I'm not sure it couldn't get very far. States regularly have taken over power utilities for instance with nary a whisper. I.e. I don't think the constitution would outright ban it if there was a good reason to do it.
As for amending being difficult, I consider that a good thing: the crazies who periodically have power (e.g. religious right) can't permanently enshrine horribly bad things in the constitution.
But here, you run into problems of scale (esp. acute in things like the Great Depression). And in any event, if having a third of Americans malnourished, poorly housed and clothed were not such an event as you describe, then I'd argue that there are no such events. Fai de bèn a Bertrand, te lou rendra en cagant
