Back then they had state level and federal level defense councils. People would get reported to the authorities for all sorts of things. If you didn't donate to the red cross you would get on the list.
They also would instruct the pastors of churches to disseminate messages and those that didn't were on the list as well. This is before mass communications took hold. Most folks got their news through word of mouth or gatherings.
What about newspapers? They weren't invented in the 1930s.
Revolutionary War propaganda famously included various pamphlets, editorials, and self-published periodicals (Thomas Paine, The Federalist Papers, etc.).
It was high. America is historically one of the more educated countries. During the civil war literacy among native born whites was over 90%. By WWI I believe it was over 95%, and by WWII it was nearly universal among native born adults.
They also would instruct the pastors of churches to disseminate messages and those that didn't were on the list as well. This is before mass communications took hold. Most folks got their news through word of mouth or gatherings.