There is very little in this song that relates to government in a detailed way. Instead, the song is simply about a general idea. This is the idea that America's system of government and its society are based on providing freedom to all individuals.
The song does not talk about any of the major aspects of our government. It does not talk about separation of powers or checks and balances or even about democracy. Instead, all it says is that Americans are free. This is a way of saying that our government is a limited government that must protect our rights. It is a way of saying that there are many things that the government may not do (as laid out, for example, in the Bill of Rights) because they would take away our freedoms.
This song, then, is a song about the basic idea that America's political system stands for freedom.