My colleague John Samples, a distinguished political scientist and scholar of American politics, writes to me to pithily explain the discretionary/non-discretionary distinction:
Discretionary spending goes through the annual appropriations process. Such spending has to be approved each year, in form at least. Non-discretionary spending has permanent appropriations which are determined by demographics in tandem with specified entitlements. Non-discretionary spending can be changed but only by reopening the authorization for the program. Revising an authorization is quite difficult to do politically. This is not a principled distinction. It is just a political difference. Presumably constituencies of non-discretionary spending are more powerful than those supporting discretionary spending.
So the real distinction has to do with the political ease of exercising discretion, and not the legal possibility of exercising discretion.
What, then, would be a descriptively accurate way of making the distinction? Suppose a responsible journalist wanted to convey the facts as they actually stand rather than reinforce the political choice to make the distinction in this confusing way? Spending that is “annually appropriated” versus spending that is “authorized until revised”? That would be accurate, wouldn't it? (Please come up with something better!) But “authorized until revised” leads you to think immediately of the possibility of revising it. “Non-discretionary” or “mandatory” leads you to think that that the spending is somehow legislatively off-limits, which is of course false and so misleading.
This is one of those cases where I think language must have political effects. So here's one for you, George Lakoff. The labeling of Social Security and Medicare spending as “non-discretionary” encourages the sense that the programs are part of what Cass Sunstein calls “the second Bill of Rights” — that they are underwritten by some kind of legal guarantee that goes beyond the will of the current congressional majority, when in fact reopening authorization, though politically difficult, could in principle happen at any time. Strangely enough, I think the “non-discretionary” frame is partly what led Social Security reformers to attempt to motivate reform as necessary to avert a “crisis.” It's non-discretionary! Like a barrelling train with the brakes out heading for a cliff! Here is out plan to use massive dirigibles to lift the train aloft! However, by successfully rebutting the “crisis” meme by pointing out how easily the benefit formulas can changed–the brakes work fine, thank you–defenders of the status quo loosened the sense of guarantee crucial to the social insurance frame. So what we saw were Democrats simultaneously arguing that we can just change the formulae whenever, so no worries, while at the same time fretting over how certain changes, like progressive indexing, would dislodge the sacred myth of universal social insurance.
By the way, I just glanced at Jason Furman's short paper about progressive indexing. I really like progressive indexing.
I also like mandatory retirement accounts for paternalistic reasons that are also sort of libertarian. Means-tested benefits for old people is a better idea than our stupid current system, but would encourage too little retirement savings. Why? Old people are so politically powerful that these benefits will be too high to make saving rational. So forcing people to transfer their own money to their future selves prevents them from later forcing others to transfer them money when old.