I disagree, it is not something real or tangible. I'm all for defunding NSA, but it's not like a regular business which you can boycott by not giving them money. You have to go and ask permission from the government to not give the money (which they previously extracted from you by force for the "good of society") to some of the government agencies. It's pretty much like going to NSA itself and ask them to defund themselves. Voting is just a suggestion, it's not binding. Presidential candidates promise stuff, get votes and then are not obliged to deliver what was promised. It works the same way in every country today.
Real and tangible way to defund NSA is this:
1. Withhold your taxes.
2. Protect yourself against the police and the military who will try to extract them by force (possibly by having crowdfunded guards).
3. Switch from using US Dollar as most of the money government generates comes from inflation (gov sells "bonds" that it will never repay in exchange for new money). Since all national currencies are inflationary and controlled by similar institutions all over the world, only Bitcoin is a good alternative. Or gold, if we can protect the vaults properly and build trust in a company that keeps it (but history shows it doesn't work).
4. Pay only what you think is fair and where you think it's fair. E.g. if you like social security, pay there directly as much as you want.
Only voluntary payments will guarantee that people who you don't like get as much money as someone is willing to give them explicitly and voluntarily. You should not ask for permission to not participate in what you don't approve.