In coming days, we will publish articles by members of the Editorial Board and supplementary material that will examine these questions. We invite readers to offer their ideas, and we will report back on their responses, pro and con.

Changing it wouldn’t even require an act of Congress — the attorney general or the secretary of Health and Human Services could each do so — although the law should be changed to make sure that future administrations could not reimpose the ban.

According to F.B.I. data, more than half of all violent crimes nationwide, and four in five property crimes, went unsolved in 2012.

In 1930, Congress consolidated the drug control effort in the Federal Bureau of Narcotics, led by the endlessly resourceful commissioner, Harry Jacob Anslinger, who became the architect of national prohibition. His case rested on two fantastical assertions: that the drug caused insanity; that it pushed people toward horrendous acts of criminality.

Its downsides are not reasons to impose criminal penalties on its possession, particularly not in a society that permits nicotine use and celebrates drinking.

regular users can have blood concentration levels of THC, the psychoactive ingredient in cannabis, well over Colorado’s legal limit of five nanograms per milliliter and drive perfectly well, and marijuana can be detectable weeks after a high has worn off ... there is still no evidence that THC, even in large amounts, is even close to being as lethal as alcohol or tobacco.

The experiences of Colorado and Washington, where sales of recreational marijuana started this year, will prove instructive. While there are important differences in their approaches, both states have licensed businesses to grow, process and sell marijuana while imposing strict rules and high taxes on them.