Actually a lot. Why are politicians like Kennedy proposing these things? Because they know that some Bitcoin speculators like the idea, so they can dump their coins once the "government pump" took the price to extreme heights.
So what you can do is to not vote people who propose that, and clearly signalise that many Bitcoiners aren't interested in a government-controlled Bitcoin.
Of course in countries like China this isn't possible that easy. But even there, you can raise your voice to some extent.
I was not talking about stopping them through a political process such as an election. Election is a 'scam' in so many places in the world and the most popular or incumbent candidate always find a way to win, mostly through corruption i should add, so there is still a high chance that even if most of the bitcoin community don't vote for such candidates, they would still be victorious in their different countries.
I don't even think the bitcoin community is that large yet, so their votes cannot decide the outcome of an election, and there is no way for bitcoiners to stop a president who decides to accumulate so much BTC's.