The same system that allowed lunatic-fringe Democrats to rise in the party is in the Republican Party. Delegates become delegates at seemingly unimportant, backwater party meetings. They then vote at local and state conventions to endorse candidates, elect party leaders and set party policy. These delegates are often highly motivated to go to these meetings but more sensible people often have other things going on in their lives or more important things to do. In that void, the extremists win the day and, like AOC, come to have their day in the sun.
This dynamic is intensified by the gerrymandering the elected officials do to draw district lines that are mostly red or mostly blue so as to make their own districts safe for themselves.
