Parts of a campaign rally are reflected in teleprompters as President Obama speaks in Golden, Colorado on September 13, 2012.

[REUTERS/Kevin Lamarque]

With Obama facing a stiff challenge from Mitt Romney in the election, his chances of winning the key state of Colorado could hinge on marijuana legalization, supported by a growing number of Americans.

At issue is whether Obama will get a boost from young voters expected to be among the most enthusiastic backers of a Colorado ballot initiative that would legalize possession of up to an ounce of pot for recreational use - and give the state the most liberal marijuana law in the nation.

READ MORE: Marijuana initiative could make or break Obama in Colorado

Credit: Students and others smoke marijuana at a pro-marijuana rally at the University of Colorado in Boulder, Colorado, April 20, 2012. REUTERS/Rick Wilking