WASHINGTON -- Longshot GOP presidential candidate Gary Johnson attacked frontrunner Newt Gingrich for supporting the death penalty for marijuana smugglers even though he has admitted to smoking the drug himself during graduate school.

Gingrich "proposed the death penalty for marijuana -- for possession of marijuana above a certain quantity of marijuana -- and yet he is among 100 million Americans who smoke marijuana," Johnson told MSNBC’s Alex Witt over the weekend.

An outspoken critic of federal drug control policy, Johnson added he "would love to have a discussion with [Gingrich] on the fact that he smoked pot, and under the wrong set of circumstances, he proposed the death penalty for something, potentially, that he had committed?"

That's not quite right. Even under Gingrich's draconian proposal, nobody could be sentenced to death for smoking pot. But Johnson does effectively highlight one of the more outrageous pieces of drug policy to be introduced before Congress, and pushed by the GOP presidential front runner no less. In 1996 the former House Speaker sponsored the Drug Importer Death Penalty Act, under which importing more than two ounces of certain illegal substances -- including marijuana -- can be punishable by life imprisonment or the death penalty.

Johnson, the former New Mexico governor, has been open with the media about his own experiences smoking pot. After a paragliding accident in 2005, Johnson asserted "marijuana really helped [him] deal" with the pain, and in an interview with the New Republic he joked, "I never exhaled. His policy position on medical marijuana flows naturally from that experience.

But Gingrich, who smoked pot while in graduate school in the '60s, wants to have it both ways.

"That was a sign we were alive and in graduate school in that era," he told New York magazine in 1995 of his illegal drug use. And in 1982, he penned a letter to the Journal of the American Medical Association calling for the legalization of medical cannabis. Federal law, he wrote, "continues to define marijuana as a drug 'with no accepted medical use,' and federal agencies continue to prohibit physician-patient access to marijuana. This outdated federal prohibition is corrupting the intent of the state laws and depriving thousands of glaucoma and cancer patients of the medical care promised them by their state legislatures."

While it's hard to pinpoint exactly when Gingrich went from calling for marijuana legalization to introducing legislation sentencing pot smugglers to death, his peculiar evolution certainly merits an explanation.

"See, when I smoked pot it was illegal," he reportedly told the Wall Street Journal's Hilary Stout in 1996, "but not immoral. Now, it is illegal AND immoral. The law didn’t change, only the morality... That's why you get to go to jail and I don't."

WATCH Mediaite's video of Johnson's remarks: