If Apple started building all their products, or at least the iPhone and iPad in the US, would we see less leaks?

I doubt it. Supply chains just involve too many people. Apple can keep secrets when it's inside Cupertino, but I can't envision a way apple could do the same with a massive hardware assembly system that could work at the scale, and for the price, that would be required.

It totally depends on who's running the plant.

If it was Apple owned & operated, they would be able to lock everything down quite a bit more than is currently possible. For any outsourced manufacturing, US or foreign based, it's a lot harder because it's not your facility. Apple can issue rules and guidelines, but at the end of the day, they're just a client.

Thinking through the US options:
On the one hand, Apple would have stronger contracts and US based legal powers to put the fear of God into anyone who would even think about leaking. On the other hand, information is always going to get out.

It's impossible to completely shut down leaks, but if the manufacturing were based in the US, I think they would slow down to a trickle.

That brings up a broader thought (and I have a feeling apple has evaluated this already): whats the cost balance between bringing manufacturing closer to home + beefing up security versus whatever "losses" they faced due to leaks?

And what losses have they faced? lesser sales? probably not. Competitors getting tipped off? Not in this industry, plus now they have proved litigation will handle that for em.

I'd venture to say a *limited* amount of leaks are more helpful than harmful, in buzz generation etc. Now the only question is whether not the current amount of leakage is into the harmful zone or still in the helpful zone.