You put the organization that funds it at arm's length from the actual government. Positions in it, all the way to the top, are regular jobs that get hired for

You put the organization that funds it at arm's length from the actual government. Positions in it, all the way to the top, are regular jobs that get hired for, not political appointments. Write something into its charter about the funding never being conditional on content, only on some proof of ability. Make the amount of funding (for the organization as a whole) indexed to something meaningful—like inflation, or Congressional salaries, or something like that, with a multiplier based on national population—rather than having to be appropriated annually or at some fixed level. It's not perfect, and it can't be, because Congress can always decide they don't like what it's doing and go back and meddle. But there are many safeguards that can be put into place to reduce the amount of direct government interference with such an organization—and those above are just what I could come up with off the top of my head in a couple of minutes. Given a committee with an actual mandate to assemble something like this, and people who are genuinely interested in doing so, I'm sure a much more solid framework could be ironed out.