MARIJUANA is now legal under state law for medical purposes in 16 states and the District of Columbia, encompassing nearly one-third of the American population. More than 1,000 dispensaries provide medical marijuana; many are well regulated by state and local law and pay substantial taxes. But though more than 70 percent of Americans support legalizing medical marijuana, any use of marijuana remains illegal under federal law.

When he ran for president, Barack Obama defended the medical use of marijuana and said that he would not use Justice Department resources to override state laws on the issue. He appeared to make good on this commitment in October 2009, when the Justice Department directed federal prosecutors not to focus their efforts on “individuals whose actions are in clear and unambiguous compliance with existing state laws providing for the medical use of marijuana.”

But over the past year, federal authorities appear to have done everything in their power to undermine state and local regulation of medical marijuana and to create uncertainty, fear and confusion among those in the industry. The president needs to reassert himself to ensure that his original policy is implemented.

The Treasury Department has forced banks to close accounts of medical marijuana businesses operating legally under state law. The Internal Revenue Service has required dispensary owners to pay punitive taxes required of no other businesses. The Bureau of Alcohol, Tobacco, Firearms and Explosives recently ruled that state-sanctioned medical marijuana patients can not purchase firearms.