There's also an academic debate about what triggers large-scale changes in institutions (internal forces, external shocks, etc.). Democratic congressional leadership is definitely facing an external shock (Trump) but so far this has only forced a kind of doubling down on existing/weak tea D politics
In other words, by all means blame Schumer/Jeffries for being blind to both the risks they/we face and to the (small) power they do wield. But it's also helpful to appreciate that they have made themselves prisoners of a set of rules that got them where they are, even if it is destroying them now