Via Kevin Drum (“Random Debate Thoughts (So Far),” Political Animal, Washington Monthly, 13 December 2007) a new factoid that Barack Obama is brandishing:

Reducing obesity to 1980 levels will save Medicare $1 trillion.

I’m too busy right now to go and fact-check this before passing it along, but when I considers the sheer number potentialities like this out there in the realm of possibility, I am reminded of Paul Krugman’s admonition regarding how to think about the financing of the U.S. welfare state (“Social Security Scares,” The New York Times, 5 March 2004):

By all means, let’s plan ahead. But let’s set some limits. When people issue ominous warnings about the cost of Medicare after 2077, my question is, Why should fiscal decisions today reflect the possible cost of providing generations not yet born with medical treatments not yet invented?

There is the pragmatic reason that the sooner we act, the less we have to do, but I think Mr. Krugman is right to suggest that there are just too may unknown unknowns — to borrow a Rumsfeldism — to seriously plan for 2077.