(Nick Adams/Reuters)

The Justice Department will not challenge Washington and Colorado's new laws that legalize marijuana use among adults. Huffington Post's Ryan J. Reilly and Ryan Grim report:

A Justice Department official said that (Attorney General Eric) Holder told the governors in a joint phone call early Thursday afternoon that the department would take a "trust but verify approach" to the state laws. DOJ is reserving its right to file a preemption lawsuit at a later date, since the states' regulation of marijuana is illegal under the Controlled Substances Act.

The Department also, per Reilly and Grim's report, sent a three page memo to governors of all states outlining federal priorities for enforcing marijuana laws. This included "the distribution of marijuana to minors" and "drugged driving and the exacerbation of other adverse public health consequences associated with marijuana use."

Regulating recreational use of marijuana is not on that list.

Justice's decision comes at a time when public support for marijuana is at - excuse the pun - an all time high. Gallup's most recent poll showed that 48 percent of Americans think marijuana ought to be legalized, up from 34 percent about a decade ago. This still isn't a majority of Americans, but its edging pretty close.

Now, Colorado and Washington will likely move forward with the actual business of regulating marijuana–which is actually a pretty difficult task. Mike Konzcal wrote a piece for Wonkblog in June, Washington was grappling with the best way to move forward, and whether its better to have large players dominate the marijuana industry–or smaller businesses be on top.

As Chris Marr of the Liquor Control Board argued, “How do you prevent a Microsoft millionaire from getting this idea and deciding that — playing by the rules — they’re going to dominate the market?” And if that is the concern, what can economics inform us about how this new market should be set up?

Colorado has moved forward with setting a legal limit on active THC - the psychoactive chemical in marijuana - in the blood stream while driving, something akin to a blood alcohol limit. In other words, the state has had to figure out what counts as too stoned to drive.

Those who do not reside in Colorado and Washington may also notice an impact of legalized marijuana in those states: One expert I spoke with late last year predicted that the legal supply in these two states would likely drive down marijuana prices across the country.