Sen. John McCain, R-Ariz., listens during a Senate Foreign Relations Committee hearing on Thursday, Sept. 3, 2013, in Washington, D.C. (BRENDAN SMIALOWSKI/AFP/Getty Images)

Sen. John McCain, R-Ariz., told attendees of a Tucson town hall meeting Thursday that the United States might want to legalize marijuana.

McCain made the relatively unprompted call for drug policy reform when an attendee asked why the U.S. should intervene in Syria's civil war, but not in Mexico, where drug cartels are locked in a deadly conflict with the government and each other.

The 2008 GOP presidential nominee then launched into a lesson about economics to explain drug smuggling and said he was open to legalizing marijuana.

"Let me just say what's going on in Mexico, in my view, to some degree, is our responsibility... because we're creating a demand for drugs in this country and when there's a demand, there's going to be a supply," McCain said.

"Legalize it!" some crowd members mumbled.

"Well, maybe we should legalize it," he responded, "we are certainly moving that way so far as marijuana is concerned, but I will respect the will of the people."

He then hammered home his economic explanation of drug smuggling, saying: "They are bringing these drugs across to our country because there's a demand for them and there's going to be a supply wherever there is a demand."

In November, residents of Washington state and Colorado voted to legalize marijuana by wide margins. State-licensed stores will begin serving adults over the age of 21 next year. Advocates of marijuana legalization say legitimate businesses will smother the black market and the violence that accompanies it.

"My urging is that this country engage in a conversation about drugs, about the punishment for drugs," McCain added. "A huge percentage of the people in prison today are drug related crimes. I'm not saying that's good or bad, but I am saying that we need to have a national conversation."

McCain spokesperson Rachael Dean did not respond to a U.S. News request for clarification.

Watch footage of McCain's town hall, via KVOA-TV. His comments on marijuana begin 29 minutes in: