I'd start with foreign aid and our sending money and supplies to countless other nations. I get that other nations are sucking worse than we are, but we can't have it both ways. We can't complain about how broke we are and still send money to other nations.
I'd also recover the vast majority of our armed forces overseas and bring them back to their home stations - and ideally back to CONUS. We have not been tasked by anyone to be the world police, and its not something we should be jumping on by ourselves. We need to enter a period of national regrouping and recovery where we focus on education, production and trade - not "defense."
Another area we can save money is by not buying a whole new "set" of the latest and greatest war machines. Do we really need 2000+ F-35s or F-22s? No, we really don't. I'm all for continuing R&D and making more better fighters and other systems, but we don't need to fully field each iteration. Let's save some of that $$ we don't spend buying a new fleet and put it back into making the next system better. There is no other nation on the planet capable of going toe to toe with the US in the air, on the ground, or in the water - what is the purpose of increasing that disparity? The trade off is that we are losing the race in education, cyberspace, and space exploration. We're trading long term benefits for short term security. That will be what puts the US at the mercy of other nations in the next century.
Foreign aid costs us billions every year, to countries we receive little to no tangible benefits from in aiding. Call me heartless, but we cant afford to give right now, we need to focus on our own country. Thank god other countries havent called in their debts.
I would then look at changing how the government conducts business in general. I would look at contracting to private companites to handle the delivery of services to the people. It would actually be cheaper and more efficient to hire companies that would have a profit motive that would reduce fraud and provide the people with better service where someone who is terrible at their job can actually be fired instead of lingering around and collecting a pension just because they waited out the clock (For example it is possible to conduct many DMV services here in California through the AAA and they are friendly and helpful, with much less waiting).
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