I was going to say he can't be the first republican to come out in favor of marijuana being legal. But I can't really find any decent list of politicians advocating for marijuana being legal from the big two parties.
I think Ron Paul did too. But yeah, Gary Johnson doesn't count as a presidential candidate, or counts as much as any Libertarian Party candidate ever does. He went into the GOP primaries being yet another voice for cutting spending and balanced budgets (too similar to the other candidates, and no clear economic plan), while being very liberal on the social issues (too similar to Paul, except on abortion). If Ron Paul hadn't run again, he would have gotten more attention. He just doesn't have a unique message. If he was smart he would have dropped out after NH, but stay in the GOP, to run again in 2016.