The only thing you need to remember is that political parties, by law, cannot restrict candidates from running under that party banner. Superdelegates are how the Democratic Party leadership attempts to skirt this and put its thumb on the scale, but after the Clinton-Sanders debacle, their power was diminished.
An ideological takeover of the party is possible. It just requires progressive candidates to get elected.
The only thing you need to remember is that political parties, by law, cannot restrict candidates from running under that party banner. Superdelegates are how the Democratic Party leadership attempts to skirt this and put its thumb on the scale, but after the Clinton-Sanders debacle, their power was diminished.
An ideological takeover of the party is possible. It just requires progressive candidates to get elected.