Maryland Gov. Martin O'Malley (D) on Monday signed a bill into law that decriminalizes the possession of small amounts of marijuana.

In the process, O'Malley becomes the rare potential presidential candidate who has deregulated the drug -- something that is sure to be something of a subplot if he runs in 2016.

Maryland joins about a dozen other state that have also decriminalized the drug, making possession of small amounts more akin to a traffic violation than a criminal act.

Despite a large national shift toward marijuana legalization, politicians are still generally wary about legalizing or decriminalizing it. Just two states -- Colorado and Washington -- have legalized it fully.