A representative republic is the system we have in the US, which is by definition not a democracy. They're two very different concepts, and they are mutually exclusive.
This is basic civics. It's taught, or I hope it's still taught, in grade school. It's not controversial, it's not surprising, it's fact.
It was designed to be difficult to change because democracies always fail when the majority decides the rule of law is no longer important.