“Teachers’ unions are the core of the Democrat Party; they own it”
That’s largely true, along with militant secularists, government aid recipients, and ethnic identity demagogues.
Nobody gets as much from the party as the teachers’ unions; welfare was reformed, affirmative action has been successfully challenged in some courts, but the teachers’ unions keep getting more & more money. The Dems don’t control the unions or cater to them; they are the political arm of the teachers’ unions.