Consider this for an illustration of just how much society has changed in the past few generations: New data shows that, for the first time ever, more Americans use marijuana than tobacco.

It's positive news from a public health standpoint. Whatever the legitimate concerns about the U.S. becoming a pot-head nation, weed is demonstrably safer than cigarettes. Yet federal law continues to treat pot like the dangerous illicit drug that past generations long thought it was. It's time for that to change.

A study funded by the National Institutes of Health found that marijuana-use and cigarette-use trends have gone in dramatically opposite directions in recent decades. The study found 16% of Americans today use marijuana, more than twice the percentage as in 1999. Almost half of Americans today say they have tried marijuana at some point, compared to about a third who had tried it as of 1999. Reaching back further, to 1969, just 4% of Americans said they had tried pot.

Cigarette use, meanwhile, is plummeting. Just 11% of Americans say they currently smoke, compared with 23% in 1999 and 40% in 1969.

Perhaps not surprisingly, those overall numbers are driven largely by an even more dramatic divergence of vices among young people, with those 18 to 34 preferring pot to cigarettes by double-digit percentages.

But America's largely geriatric political leadership still resides far in the past in terms of federal marijuana policy, even as states' laws increasingly embrace modernity. Missouri and 36 other states have legalized medical marijuana, with 19 states allowing it for recreational use as well. Yet in the eyes of the federal government, it remains a Schedule 1 drug — the most tightly regulated category that includes heroin — under the Controlled Substances Act of 1970. Which, as the above data illustrates, was a time of far different societal attitudes than today.

The federal government's answer to this cannabis conundrum has been to continue the federal prohibition on pot while declining to enforce it in states that have legalized it. This solution may be practical, but it undermines the whole concept of federal supremacy. The gun extremists who control Missouri government have been rightly condemned for claiming the state can simply ignore federal firearms laws — yet the only way state legalization of pot works is for the states and the District of Columbia to mutually accept exactly that kind of scenario.

Meanwhile, banks and other institutions that operate under federal laws are put in an untenable situation when it comes to interacting with states' legalized marijuana industries, given that such interactions are technically federal crimes.

Maintaining a federal contraband law that everyone agrees can be ignored in most of the country fosters disrespect for the law. The solution isn't complicated: Federal law regarding pot should be updated to reflect where most of America is on the issue today.