It seems that no presidential debate this year would be complete without denunciations of the drug laws, which, it is alleged, result in long prison terms for thousands of people, disproportionately African Americans, who are guilty only of low-level offenses, thus fueling "mass incarceration."

At the last Republican debate, on Sept. 16, former Hewlett-Packard chief executive Carly Fiorina charged that "two-thirds of the people in our prisons are there for nonviolent offenses, mostly drug-related." Apropos of former Florida governor Jeb Bush's admitted youthful marijuana use, Sen. Rand Paul (Kentucky) observed that "there is at least one prominent example on the stage of someone who says they smoked pot in high school, and yet the people going to jail for this are poor people, often African Americans and often Hispanics, and yet the rich kids who use drugs aren't."

When Democrats faced off Tuesday night, Sen. Bernie Sanders (I-Vermont) said he is for marijuana legalization, "because I am seeing in this country too many lives being destroyed for nonviolent offenses. We have a criminal justice system that lets CEOs on Wall Street walk away, and yet we are imprisoning or giving jail sentences to young people who are smoking marijuana." "I agree completely with the idea that we have got to stop imprisoning people who use marijuana. . . . We have a huge population in our prisons for nonviolent, low-level offenses that are primarily due to marijuana," the front-running former secretary of state, Hillary Clinton, chimed in.

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Too bad this bipartisan agreement is contradicted by the evidence. Fiorina's numbers, for example, are exaggerated: In 2014, 46 percent of all state and federal inmates were in for violent offenses (murder, rape, robbery and aggravated assault), according to the latest Justice Department data. And this is a conservative estimate, since the definition of violent offense excludes roughly 30,000 federal prisoners, about 16 percent of the total, who are doing time for weapons violations.

Drug offenders account for only 19.5 percent of the total state-federal prison population, most of whom, especially in the federal system, were convicted of dealing drugs such as cocaine, heroin and meth, not "smoking marijuana." Undeniably, the population of state prisons (which house the vast majority of offenders) grew from 294,000 in 1980 to 1,362,000 in 2009 - a stunning 363 percent increase - though it has been on a downward trajectory since the latter date.

But only 21 percent of that growth was due to the imprisonment of drug offenders, most of which occurred between 1980 and 1989, not more recently, according to a review of government data reported by Fordham law professor John Pfaff in the Harvard Journal of Legislation. More than half of the overall increase was due to punishment of violent offenses, not drugs, Pfaff reports.

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Reviewing data admittedly drawn mostly from Northern "blue" states, Pfaff determined that "the median stay in prison for a drug offender is generally about a year," and that "relatively few people appear to be in prison on marijuana charges" - fewer still for simple possession.

Given the relatively small share of drug offenders, ending the war on drugs would not significantly alter the racial disparity in incarceration rates, contrary to the conventional wisdom.

Blacks make up 37.5 percent of all state prisoners, about triple their share of the population as a whole, according to the Justice Department. If we released all 208,000 people currently in state prison on a drug charge, the proportion of African Americans in state prison would still be 37 percent.

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In short, ending the "war on drugs" is not quite the panacea for mass incarceration that politicians imply.

Marijuana legalization could help reduce arrest rates, to be sure; and to the extent fewer people get busted for smoking pot, that would, indeed, cut down on the resulting undue negative personal and social consequences.

Otherwise, the bipartisan consensus in favor of looser drug laws is just the latest political free lunch, served up by politicians who would rather discuss anything except real public policy trade-offs.

Republicans and Democrats alike are propounding the crowd-pleasing notion that we can have less incarceration - saving the country billions of dollars and international shame - without risking an increase in violent crime, or other harms.

In truth, if we released all 300,000 drug offenders from state and federal prison, the U.S. incarceration rate would still be far higher than it was three decades ago, and far higher than the rates of other industrial democracies.

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The only way to lower it dramatically would be to reduce the frequency and duration of imprisonment for violent crimes, while continuing to reduce violent crime itself.

If any of the candidates has a plan to do that, he or she should speak up.