New Jersey Governor Chris Christie is an outspoken opponent of legalization. In July, he told residents of legal states to enjoy their recreational cannabis while they can because he plans to enforce federal anti-cannabis laws in all 50 states if elected president in 2016.

He may also present a major roadblock in the movement to change cannabis from a Schedule I to a Schedule II drug so that it can be tested and prescribed more by researchers and physicians.

At a campaign event in Iowa Oct. 21, Christie had an argument with Shelley Van Winkle, a nurse and veteran of the First Gulf War. He told her the president can't reschedule cannabis; only an act of congress can.

Here's the full exchange:

Does congress alone hold the power to change cannabis laws?

No, according to former Attorney General Eric Holder, who spoke on the issue with a Huffington Post reporter during the 2012 White House Correspondent's Dinner. The reporter mentioned an April 2012 Rolling Stone interview with Jann Wenner and Barack Obama, in which the president shared sentiments on rescheduling similar to Christie's stance:

"I can't nullify congressional law. I can't ask the Justice Department to say, 'Ignore completely a federal law that's on the books.' What I can say is, 'Use your prosecutorial discretion and properly prioritize your resources to go after things that are really doing folks damage.' As a consequence, there haven't been prosecutions of users of marijuana for medical purposes."

Attorney General Holder told The Huffington Post Obama's comments were misleading because the president has the executive authority to tell the Drug Enforcement Agency (DEA) to remove marijuana from Schedule I categorization, and therefore recognize its medical use.

The DEA is responsible for the drug scheduling system. Organizations can petition the DEA to reschedule marijuana. But so far it has resisted these calls, and the DEA's acting administrator, Chuck Rosenberg, doesn't plan to change the organization's position on cannabis.

However, the president can order the rescheduling, according to Holder. He also has the authority to dismiss the head of the DEA and appoint a replacement more open to the idea.

'The Rebuttal' is a regular feature that takes the statements of politicians and tests them against the facts at hand. Do you have suggestions for statements we should fact-check. Leave a comment below. Twitter: @civilized_life. Facebook: Civilized

h/t Huffington Post, Politico, Think Progress, Rolling Stone