During Tuesday’s Democratic debate, the candidates were asked about their stances on marijuana legalization, and both frontrunners, Hillary Clinton and Bernie Sanders, used it as an opportunity to talk about excesses of the criminal justice system. Sanders said he supported legalization, noting that he’s seen “too many lives being destroyed for non-violent offenses.” Clinton did not take a stance on legalization (except for medicinal use), but added: “I agree completely with the idea that we have got to stop imprisoning people who use marijuana...We need more states, cities, and the federal government to begin to address this so that we don't have this terrible result that Senator Sanders was talking about where we have a huge population in our prisons for nonviolent, low-level offenses that are primarily due to marijuana.”

While the exchange provided one of the only substantive criticisms of criminal justice during the debate, Clinton relied on a fallacy about who, exactly, is filling state and federal prison beds. Yes, many are arrested for having weed (a disproportionate number of whom are black and Latino), but few are spending time in prison for it.

In 2014, only 3.6 percent of state inmates were in prison for possession of any drug (the Bureau of Justice Statistics does not break down drug offenses by substance). The U.S. Sentencing Commission offers another snapshot of how many people are being prosecuted for pot: Of 21,907 cases sentenced under federal drug guidelines in fiscal year 2014, only .3 percent were for marijuana possession. Roughly 18 percent of those drug sentences were for trafficking marijuana.

Urging leniency for the lowest-level offenders has been a theme for candidates in both parties. GOP contender Carly Fiorina also made the leap from marijuana legalization to overstuffed prisons in the Republican debate in September: “Two-thirds of the people in our prisons are there for non-violent offenses, mostly drug related. It's clearly not working,” she said. In fact, only 20 percent of state and federal prisoners are behind bars for any kind of drug violation.

As TMP’s Dana Goldstein pointed out, any attempt to cut incarceration by as much as 50 percent — the target of some reformers — will require shorter sentences not just for marijuana, not just for drugs, and not just for crimes considered non-violent. But that’s not an easy sell during a highly competitive campaign season.