Likewise, Congress can't just pass a law to spend 20% less without identifying exactly what it is going to spend less on and how. Getting people to agree on those particulars is the problem.
What makes it worse is that the things you might get wide agreement on cutting generally are things that would save negligible amounts of money. Also, even people who care a lot about the government (one way or the other) generally aren't willing spend time learning all the details of what the government is spending money on. Its really complicated and boring and I think people (especially us hn readers) would rather think of the problem at a higher level of abstraction (and in greatly simplified terms). Unfortunatley that just isn't helpful at this point
If majority of voters want to cut government spending in more than 50% of areas, then spending would be cut.
In the list you provided I'd say everything should be cut. Say, 10%/year cut until spending is at least 50% lower.
My personal preference would be not to cut interstate highway system too much, but everything else deserves at least 50% cut in the next 10 years.