New Jersey Governor Chris Christie (R) said earlier this week that he'd prosecute marijuana users if he became president.

"I will crack down and not permit it," Christie said in a radio interview with Hugh Hewitt. "Marijuana is a gateway drug. We have an enormous addiction problem in this country. And we need to send very clear leadership from the White House on down through the federal law enforcement. Marijuana is an illegal drug under federal law. And the states should not be permitted to sell it and profit from it."

This isn't the first time the Republican has criticized marijuana legalization. Last year, he insinuated that it's better to live in New Jersey than Colorado, where medical and recreational marijuana is legal, saying in his monthly Ask the Governor radio program, "See if you want to live in a major city in Colorado, where there are head shops popping up on every corner, and people flying into your airport just to get high. To me, it's not the quality of life we want to have here in the state of New Jersey. I think legalizing marijuana is the wrong thing to do from a societal perspective, from a governmental perspective."

The gateway drug myth.

Although Christie is certain that marijuana leads Americans toward more destructive substances, this "gateway drug" notion of marijuana has been challenged by science. In 1999, the Institute of Medicine of the National Academy of Sciences published a report that found "[t]here is no conclusive evidence that the drug effects of marijuana are causally linked to the subsequent abuse of other illicit drugs."

In 2010, researchers at the University of New Hampshire conducted a study that found marijuana is only a gateway drug in specific situations and not bound to destroy the lives of everyone who tries it once.

"There seems to be this idea that we can prevent later drug problems by making sure kids never smoke pot," Dr. Karen Van Gundy, associate professor of sociology at New Hampshire and study researcher, told CBS News. "But whether marijuana smokers go on to use other illicit drugs depends more on social factors like being exposed to stress and being unemployed - not so much whether they smoked a joint in the eighth grade."

In the report, Van Gundy and Cesar Rebellon said politicians should take this information into account when dealing with the nation's drug problem, "In light of these findings, we urge U.S. drug control policymakers to consider stress and life-course approaches in their pursuit of solutions to the 'drug problem.'"

Research also suggests marijuana is fairly harmless compared to alcohol. A Scientific Reports study published earlier this year concluded alcohol was 114 times deadlier than pot. Researchers compared lethal ingestion levels of alcohol, cocaine, heroin, tobacco, marijuana, ecstasy, and meth and found that marijuana was the only substance with a low death rate:

WaPo

Where Americans stand on marijuana.

An overwhelming number of young conservatives are in favor of marijuana legalization. A Pew Research Center survey published earlier this year found six in ten Millennial Republicans support marijuana legalization. Nearly half of Republican Gen Xers support it as well, and 38 percent of conservative Baby Boomers expressed support for legalization:

Pew Research Center

How his Republican competition stands on marijuana.

If Christie decides to run in 2016, one of his Republican contenders will challenge him on marijuana: Senator Rand Paul (R-Ky.). Earlier this year, Paul and Senators Cory Booker (D-N.J.) and Kirsten Gillibrand (D-N.Y.) introduced a bill aiming to repeal the federal ban on marijuana.

"A little over 20 states have medical marijuana, and yet there are still federal rules that make it difficult," Paul said. "We don't want doctors to be punished for simply trying to help people...I've done a lot of effort across the aisle with Sen. Booker and Sen. Gillibrand, and I think this is an example of how Washington works."

Possible Republican presidential candidate Jeb Bush has voiced opposition to medical marijuana, a viewpoint Paul has described as hypocritical given Bush's adolescent pot use.

"[Bush] is a guy who now admits he smoked marijuana, but he wants to put people in jail who do," Paul told The Hill in January. "I think that’s the real hypocrisy, is that people on our side, which include a lot of people who made mistakes growing up, admit their mistakes, but now still want to put people in jail for that."

Presidential candidate and Texas Senator Ted Cruz, who was the first Republican to announce his 2016 run, also smoked marijuana as a youth, but has since expressed regret.

"When he was a teenager, he foolishly experimented with marijuana," Cruz's spokesperson said in February. "It was a mistake, and he's never tried it since."

Presidential contender and Florida Senator Marco Rubio has also disparaged recreational marijuana use, yet refuses to answer whether he's done it before. Regarding medical marijuana, Rubio said last year, "If there are medicinal uses of marijuana that don't have the elements that are mind-altering or create the high but do alleviate whatever condition it may be they are trying to alleviate, that is something I would be open to."

Christie isn't the only conservative presidential hopeful opposed to marijuana, but his strong feelings about the substance could hinder his chances of landing the nomination as more Republicans of different demographics support legalization.