Is America a democracy? Is it a republic? As I explained in America: Republic or Democracy?, a nation can be both. In broad terms I think it is fair to say the the United States of America is a republic that is also a democracy. Call it a democratic-republic (but also recall that some 20th century nations that styled themselves "The Democratic Republic of ..." looked suspiciously like dictatorships).
Here I want to go a bit deeper into the idea of whether the United States of America is a democracy. The long-term historical trend has been to give more groups of people the right to vote in elections. In the 20th century women and people not of European descent gained the right to vote. The voting age was also lowered to 18. This would strengthen the democratic element of our republic. However, this broadening of the right to vote does not insure that the majority view on a particular issue becomes law.
It might be fair to call America a careful, conservative democracy. Suppose a minority position becomes a majority position, as determined by polls. It may take a long time for the majority's view to become policy or law. It is possible that elected officials may realize public sentiment has changed and make appropriate changes quickly, but that seldom happens. Representatives tend to remain loyal to the groups of people that got them elected. So those who oppose the change, or at least some of them, must be voted out of office.
Elections are held every year, but most terms of office have a two year minimum. Let's focus on the national level. The House of Representatives is re-elected every even-numbered year. To get a new majority, in tune with changed public opinion, could take up to two years, depending on where in the election cycle the change of opinion took place.
But only one-third of the members of the U.S. Senate are elected every two years. Each Senator is elected for six years. So it could conceivable take six years for the new majority to emerge in the Senate. And the President can veto the work of a mere majority, so a sympathetic President would be needed, which could take four years.
Even then, as we have seen in U.S. history, the Supreme Court could find reasons to block change. Since the Supreme Court is not elected, but members are given life time appointments by the President, it can easily take a decade for a change to take place if the Supreme Court opposes it. On the other hand, on some occasions the Supreme Court, in deciding a law case brought before it, has made sweeping changes in the laws by a single ruling. These rulings may or may not reflect the sentiments of the majority of citizens.
Even the above scenario assumes an issue is important enough to be the deciding factor in elections. But issues are bundled together so that the voters cannot always get what they want. You can vote for only one person in the House of Representatives. Generally, the set up is that the choice is between a Republican Party candidate and a Democratic Party candidate. Perhaps neither candidate is willing to work for the majority opinion on a particular issue. Or voters, and those seeking their votes, prioritize a different issue (taxes, abortion rights, immigration, etc.) over the one where opinion has changed.
In fact, because of the necessity of bundling issues when voting for candidates, even when there is a clear majority on a particular issue, there may never be appropriate legislation passed on that issue.
Does that mean that the process is not democratic? I think that would be too harsh of a criticism. To a large extent it is an unintended consequence of the republican (that is, representative) structure of our government. Some states get around this problem by allowing for referenda (votes on a particular issue by all of the voters). But there is no mechanism for a national popular vote on a single issue.
Knowing that bundling is part of the mechanics of government in the United States, special interests have every reason to thwart the will of the majority by affecting how issues are bundled. Take "wasteful government spending." One person's wasteful spending is another person's job or profits. If you ask Americans if they want to "eliminate wasteful spending at the Pentagon," they will almost all say yes. But no defense contractor thinks his profit centers are wasting the taxpayers' money. You can't run for Congress with eliminating Pentagon waste as your main issue. The other candidate will just say she's against waste too. There is no election advantage in it. So it never rises to the top of the agenda of elected officials. The same is true, most of the time, of waste at other agencies. It is true that public interest groups are sometimes successful at exposing waste. Before he became President, Harry Truman is reputed to have done a good job with his Senate committee to investigate and eliminate wasteful military spending. But generally speaking, waste is part of the package.
The U.S. Supreme Court is the least democratic, most conservative of our institutions. Of course the Supreme Court couches its decisions based on its interpretation of the U.S. Constitution, which is quite difficult to amend. In reality the Supreme Court has a long record of interpreting the Constitution to suit itself. That is why the appointment of a new Supreme Court judge or two can have greater affects on American law than almost any other event. But it is important to remember that the U.S. Constitution can be amended. In the past, amending it has often had a greater affect on government than electing whole new Congresses, Presidents, or even Supreme Courts. It is surprising that so little effort is put into amending the Constitution. There are many reasons for this, but mainly it is not a priority for the major political parties. It requires a lot of hard work to get a Constitutional amendment passed, and most attempts to amend the Constitution fail.
After the Supreme Court, the national institution that most resembles an undemocratic Republic rather than a Democracy is the U.S. Senate. There are two major problems with the U.S. Senate, if the goal is democracy. One is that there are so few Senators and so many Americans. At the time I am writing the population of the United States is about 305 million, so on average each Senator could be said to represent 3 million people. In California two Senators represent 36.5 million people. When you represent that many people, who do you listen to? At the other end of the spectrum is the state of Wyoming, with a population of just over one-half million people. That means that the Senators from Wyoming can be in closer contact with their constituencies. It also means that special interests operating at the national level can put unduly significant amounts of money into the election of Senators from states with small populations. Even without interference by special interests, small-population states tend to be rural. In the U.S. Senate rural populations have far better representation per voter than urban populations. This violates the basic rule of democracy: each citizen's vote should count the same.
Finally, there is the question of money. Citizens may know very little about the citizens who are seeking public office beyond what the campaigns choose to tell them. Usually, but not always, in the United States the candidate with the most money wins. Therefore campaign donors may influence policy more than voters. Both nationally and in some states there have been attempts, broadly called campaign finance reform, to lessen this distortion of democracy. Some have been relatively successful, for instance limiting how much money any one person can give to a campaign for Congress. Others have failed, in particular the idea of publicly financing campaigns. Special interest groups try to kill or maim these laws, and if they are passed set to work to do end-runs around them. The ability of some candidates to raise more money than the other candidates could get from public financing also tend to make these laws irrelevant.
Democracy in itself accomplishes nothing. In a democracy we may have eliminated political violence, but in the struggle for control of government there can be the equivalent of an ongoing, but very civil, war. Those who work the hardest, or have the money to hire the hardest election workers and lobbyists, have an advantage over those who merely have an opinion.
There are specific structural reforms that might make America even more democratic, such as electing the Supreme Court, or recasting the Senate so that each Senator represents the same number of voters. However, already democracy is a big playing field. Individuals and groups of people have many opportunities to push for what they want. If you feel you are in a majority and yet not getting your way, the thing to do is to push harder. If you are in a minority, but feel you are in the right, you need to work harder to bring your views to others.
If you find that a wealthy minority is bribing (perhaps legally, with campaign donations or perks from lobbyists) your representatives, you should probably get yourself another representative. If a wealthy minority is bribing both major parties, help elect independent third party candidates that share your views of the problem.
Democracy is a big notion. No one institution or marker determines whether a nation has a democratic form of government, or the reality of democratic self-rule. Even in a democracy there may be widespread injustice, environmental destruction, bad cultural values, violence, economic disarray, and just plain bad decision making by fully democratic institutions. But compared to dictatorships and other forms of minority rule, democracy puts people in the best position to reform their society and governance in a peaceful way.