The President will create a task force that will review the cases of people charged with and/or convicted of marijuana possession. Anyone charged with possession of less than two ounces who is not likely to commit violent or larcenous crimes will be recommended for pardon.
It costs approximately $30,000 to incarcerate a federal inmate. Properly staffed, this program would easily pay for itself with only those savings. It is reasonable to expect additional savings from other sources.
It is unrealistic to expect a President to effectively push for decriminalization. It is reasonable to demand that a President prudently exercise his constitutional powers to preserve the liberty of non-violent perpetrators of victimless crimes.