The NEA means national emergencies aren't a simple binary state. Instead, the President invokes "emergencies" on an as-needed basis to access specific powers delegated to him by Congress, which can shut him down with a vote (and, of course, can repeal the grants of power altogether).

So it's not as if the President can say "oh noez hackers national emergency!", suspend habeas, and imprison Michal Zalewski†. Instead: Congress gave the President the authority to recognize arbitrary foreign powers as "threats" and, pursuant to the declaration of a "national emergency", to interfere with their financial transactions. That's what Obama has done here, presumably with China as the subtext.

In the wake of KindHearts, if these powers are executed against American citizens or organizations, they can be challenged and overturned on 4th Amendment grounds. (Note the powers we're talking about are, again, only meaningful in the context of foreign transactions, or assets whose beneficiaries are foreign threat actors).

† I'm not saying you said this.