It's close to 5% of total federal spending per year, but more to the point, over 10% of total discretionary spending - the spending the government actually has any control over. It's also more than 1% of your GDP. Obviously none of that compares to how expensive wars have tended to be historically, but then the US is a good bit richer than pretty much every warring nation in the past. It's still a significant factor in the budget deficit, though the budget deficit would still be problematically large without it, since yeah, the biggest problems are not with the discretionary spending so much as with the non-discretionary spending - Medicaid, but especially Social Security and Medicare. And with Bush's tax cuts that weren't accompanied by savings on the spending side to offset them.