In what ways has the constiution been democratized throughout American history? How has this democratization changed the relationship between the people and the institutions of government?
The people have much more control over the government now and are willing to demand much more from it. This has come about in part through the democratization of the Constitution. Everyone over 18 can vote now. The people get to directly elect the Senate. These are important moves towards democracy. They make people feel more as if they should control government and that government should give them more of what they want.
I agree that the Constitution has been amended to enfranchise more people. Another way the Constitution has become more democratized is by the first ten amendments. The Bill of Rights was passed very soon after, as a compromise, but they are also important because they give people rights they need in a democracy, including freedom of the press and freedom of speech.
It depends on what you mean by "democratized." If you mean that the Constitution has been made more accessible to all people, then in some ways it has been in US history. Racialized people were once excluded as persons from the Constitution because they were slaves, as were women. But now de jure people are all equal under the law, de jure have more access to the constitution. In practice, the same is true. Many were once prohibited from hiring a lawyer to exercise their legal rights. But now all people have the de jure right to a Constitutional challenge, even just a legal one. Lastly, people know more about Constitutional claims than they once did as a whole through things like the internet and teaching in schools. In that sense, the Constitution de jure is more in the hands of the people.