Entropic one? Should I ask? 
Anyway... remember, Republicans tried to get this amendment passed during the Clinton Administration, when Clinton and Republicans actually did get a balanced budget passed (yes, I give credit to both parties, specifically because each one checked against the other going crazy with spending). Anyway, the original argument against it was sensible enough... "if we want to have a balanced budget... we just need to pass a balanced budget!" The idea was that deficit spending was necessary for non-war issues.
Personally, I would like the amendment slightly more if it included national-scale ecological crises as justification for deficit spending (not thinking a global warming debate... I'm talking more about a disease spread, Katrina-level hurricane relief, asteroid impact, etc). But that's a relatively minor issue, so I won't drag it out.
That being said, there is one problem I see. US defense spending currently comprises 15+ % of budget spending. During a war, legislators and lawyers could easily make the argument that the entire defense budget is considered "war funding," in addition to any sort of internal economic spending (think about a good portion of WW2 Roosevelt spending programs, ranging from rubber research to price controls). Thus, during a war period, the entire defense budget (15% at its lowest period in the past 50 years, but as much as 49% during the 1960's) could be written off as justified deficit spending.
The other legal question would be one of defining a "war." For example, would an unofficial war be considered a war? Would the War on Terror justify Afghanistan and TSA funding going into deficit levels?
I think it's a step in the right direction, but I'd like to see clarification as to what's meant by the exception. 
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