(CNN) The United States is a democracy, which means everyone gets to vote in US elections, right? Wrong.
Who gets to participate and how easy it is for those voters to cast their ballots has been an ongoing fight since the Constitution was written.
What exactly does the Constitution say about who gets to vote? Not much. "The people" choose congressmen. States are in charge of elections and Congress can overrule them. And electors, not voters, choose the President.
That system did not last long.
There are not one or two but SEVEN constitutional amendments that deal directly with who gets to vote and how. And a lot of laws have been passed since then, too.
The 12th Amendment, passed in 1803, set out more specific rules for electors in presidential elections.
The 14th Amendment, adopted after the Civil War, said men aged 21 and over could vote unless they had joined in a rebellion or committed other crimes.
The 15th Amendment, ratified in 1870, said men could vote, regardless of their race, though African Americans were still largely discriminated against using other methods until the Voting Rights Act of 1965.
The 17th Amendment, ratified in 1913, said senators should be chosen by the people and not state legislatures. It didn't specifically say which people.
The 19th Amendment, ratified in 1920, said states couldn't keep women from voting.
The 23rd Amendment, ratified in 1961, said citizens of Washington, DC, got three electoral votes (but no representation in Congress).
The 26th Amendment, ratified in 1971, lowered the voting age from 21 down to 18, although some states let people who are 17 vote in primaries if they'll be 18 on Election Day.
Basically it took almost 200 years to get from "the people" to a system that includes citizen men, women and black voters 18 or older.
More recent debates about suffrage have been over voter suppression -- laws or practices that make it harder for people to vote -- and voter fraud.
A lot of states have imposed voter ID laws to guard against voter fraud. It's often Republicans pushing these. Republicans have also opposed the idea of a national holiday on Election Day even though (or maybe because) it would make it easier for more people to get to the polls.
Ready for some more rules?
Donald Trump has, without evidence, spread the conspiracy theory that undocumented immigrants illegally voted for Hillary Clinton in 2016.
Actually, non-citizens could vote in some states until 1928. Congress didn't actually outlaw non-citizens voting in federal elections until 1996. Today they can only vote in some local elections, mostly in Maryland and cities like San Francisco.
Puerto Ricans are American citizens so they can vote in presidential primaries and local elections. But only if they move away from Puerto Rico to the mainland US can they take part in congressional or presidential elections, in their new state of residence.
States also have vastly different rules when it comes to felons. Voters in Florida overwhelmingly said felons should get the vote back after they've paid their debt.
It sounded weird when Sen. Bernie Sanders said he thought felons should be able to vote while they're in jail. But in Vermont, felons can vote while they're there.
All of this means that our definition of "the people" is different depending on where you live. And this democracy keeps changing.