It is possible for any current governmental agency to hijack the entire system, due to their access to supercomputer infrastructures and/or immense budgets. This will however become less and less possible while bitcoin continues to grow and is already a massive and technological challenge which I do not see any governmental institutions execute proper.
I'm not so sure that's true. Given the network at all times knows the amount of nodes out there (hence the 50%+1 rule for consensus) it would be trivial for a NSA (Nation State Actor, not TLA) to stand up 50%+1 virtual nodes fast enough to gain consensus and usurp the currencies (tokens) if I understand correctly the mechanism for determining legitimate tokens from the EconTalk interview. Am I missing something here?