The move underscores how, even though marijuana possession remains illegal under federal law, state initiatives legalizing possession for recreational use in Washington and Colorado could have far-reaching consequences. As a practical matter, virtually all arrests and prosecutions for marijuana possession occur at the state level.
The Department of Justice could sue to block enforcement of the law. Thus far, the federal government has not indicated if they will directly challenge Colorado and Washington.
In 2010, over 750,000 people in the United States were charged with possession of marijuana only.