Much of that is driven by demographics. As the population ages, health care and social security spending goes up. As health care technology improves, health care spending goes up. Military spending also went up, but that's actually relatively small beer.
The long-run US federal deficit is an issue because of health care costs. Social security will push things up a bit, but only a bit (in fraction of GDP terms) Everything else, including NASA, is essentially noise.
So if you're arguing for spending to be kept at current levels, you're essentially proposing to get rid of some part of Mediare, Medicaid, or VA health (the most cost-effective health care system in the US, by the way, and 100% socialized medicine).. But here's the great part. While the cost to government might go down - your "spending" sacred cow - costs to individuals are going to go up more, because that tax-eating behemoth the federal government buys healthcare a lot more efficiently than the private sector does.
Implicit in Republican proposals to cut healthcare costs is the notion that poor people should just fuck off and die. The only "death panel" necessary is the one that checks whether your credit card is good.. Which would indeed solve the healthcare cost issues. Try articulating that in public, though.