Baradaran. For several years at least, Bernie Sanders and Thom Hartmann have both discussed the benefits of the US Postal Service offering banking services again.
A TAX on Wall Street financial speculation/transactions, that Bernie proposes to help fund college is tuition, was in place earlier and for different reasons I learned from a commenter's post here.
The tax likely began with the reforms of FDR. The transaction tax was originally imposed on banks for financial speculation in order to help fund the SEC, the Securities and Exchange Commission, the new federal regulatory agency for finance established under FDR, and headed by Joseph P. Kennedy who FDR selected for the position.
But in the 1960s there was movement to remove the tax since the federal SEC agency was fully funded by then or for other reasons. I'm not sure of the rationale.
Bernie's idea to tax Wall Street speculation to support our young people's education and invest in them and the future is an outstanding one. The banks were helped in 2009 by the people and they can return the favor as he says.