[The One and Only...]

"National emergency" would probably be somewhat defined, but still vague. If anything clearly was not listed as a national emergency, there would probably be a clause that allowed it to be considered one with a strong majority vote, like 3/4.

The deficit would be taken care of before the amendment was added, or it would simply not be considered spending for the purpose of the amendment. Of course, in order to prevent abuse, strong budget restrictions would need to be put in place as well...

Also, I errored when I said GDP. That would not be a very accurate method. So, a forumula might need to be added in, or perhaps restrictions on taxation levels.