Defense of the United States is required by the US Constitution. Defense requires military spending. Military spending is money given to the military itself as well as arms produced by non military companies and contractors.
The military industrial complex is, essentially, a mandatory relationship, though with significant problems leading to inefficiency and poor management decisions.
The way to fix this is through reform. It could be argued that the election of a private citizen with no government experience however significant experience in the private sector is evidence of actual voting in for change in the military leadership. Whether this translates to actual long term efficiency is yet to be seen.
It's throwing away your vote until it isn't. As recent as 1992 a third candidate got above 18%, and led in the polls just a few months before the election.
Either way, voting for reformist candidates (for either way you support) in senate, house and local elections goes a long way.
