He's trying to sound less moderate. Cons still disapprove of legalization at about 70%, so there's no reason for a Republican candidate to approve of it if he wants support from his base. Christie is the moderate Republican, which is crazy, but he has to compete with the hardliners like Huckabee and Santorum for support from the ultra-conservative base. This is what happened last time around. The Republicans spend so much time appealing to their base that they alienate the actual moderates and independents.
He's trying to sound less moderate. Cons still disapprove of legalization at about 70%, so there's no reason for a Republican candidate to approve of it if he wants support from his base. Christie is the moderate Republican, which is crazy, but he has to compete with the hardliners like Huckabee and Santorum for support from the ultra-conservative base. This is what happened last time around. The Republicans spend so much time appealing to their base that they alienate the actual moderates and independents.