A division of the credit union, Safe Harbor Private Banking, provides checking accounts expressly for the marijuana industry, in clear violation of federal law. Partner Colorado was originally chartered in 1931 to serve postal workers; with about $350 million in assets, it still amounts to little more than a rounding error in the state’s financial-services market. But in three years it has established itself, entirely through word of mouth, as the marijuana industry’s biggest banker. These clients deposited $931 million in 2017. No other United States bank or credit union has probably taken as much. Most of those deposits are cash, taken off the streets and thereby reducing the latent, associated threat of robbery — a threat not just to those working in the industry but also to the ordinary people around them.