[PhantomGremlin]

Maybe that's why so many US states have dramatically underfunded pension plans (meaning teachers and other pensioners might not actually get their promised pensions when they retire).

This is a very complex topic. I think it's widely agreed that the US Congress can change Social Security benefits at any time. But the pension issue varies in the states. E.g. the Illinois Supreme Court ruled that pensions were sacrosanct:

Justices cited a provision in the Illinois Constitution stating that pension benefits, once granted, “shall not be diminished or impaired.”

https://www.chicagotribune.com/news/local/politics/ct-met-il...