It is not a democracy, was never a democracy, was not designed to be a democracy. It could be considered a "prelude to a democracy if it really wishes to be and is willing to work hard to get there".
The U.S. was invented at a time of monarchy. Three things it innovated were polyarchy (a ruling class of many rather than one, a king), a written constitution (power comes from people who grant a revocable mandate of authority to the polyarchy, rather than mandate from heaven to the monarch), and one person one vote. Of course who gets to vote is not by any means democratic: you had to be citizen, be a man, be white, and own land.
It's become much more democratized since then, on paper. And it could become a democracy at any moment.
However if you look at the ethnic and economic make up of the country compared to their representatives, the polyarchy is still overwhelmingly landed elite, male, and white. The average net worth of a Congressperson is around $7 million. And there's no meaningful difference between Democrats and Republicans when that's broken down, so I'd say we have a one party system with two factions. It's distinctly non-democratic, still, in practice. And it even looks more like an evangelical prosperity theology driven church than a democracy.
But most people don't vote. And most voters, vote party line. It's a tribal system, most voters are deeply ignorant of issues. They're sufficiently happy being peasants and serfs, and having a polyarchy of lords rule them.