Why is both he and Paul running? Won't they just split the vote amongst their base?
It IS conceivable that they could both run at first to back each other in the debates and rile up supporters the other couldn't get (Johnson's pro-choice stance and focus on drugs would be useful for him), and then whoever is pollling worse would pull out and back the other. Plus, if they were both debating they could make their views look way stronger (remember how basically every debate in '08 treated Ron Paul as the weirdo? Won't fly in 2012).
Or they could just sap each others votes.
But honestly, MBD, that's not many votes to sap.
Depends. Assuming they can max out at 15% of the vote overall and the field is crowded, one on his own could conceivably snatch up a narrow victory by taking a couple of favourable states (eg. winning Nevada, placing well in Iowa/New Hampshire, winning chunks of the midwest/New Mexico/Oregon, etc). If that was a possibility, then vote-sapping would actually matter (assuming only one of them ran, the other would be basically guaranteed most of the support of the libertarian block).
Because Ron Paul has certain advantages over Johnson. He has some degree of celebrity status, so if he decides try he will hit the ground running, whereas Johnson will have to start from ground up. Furthermore, Ron Paul comes off as far more charismatic than Gary Johnson (who, to me at least, often sounds like he doesn't really believe in what he is saying). Also, he has a very strong grassroots network, whereas Gary Johnson has far less of that and isn't the kind of guy to motivate it to become strong (can you really imagine the Gary Johnson 2012 campaign raising millions with moneybombs?).
On the flip side, Gary Johnson has less of a way of alienating people, so he might be able to broaden his appeal. But then, I don't see how he could survive the primary when his big issue is the drug war and his pro-choice views are pretty strong too. He would get decimated in many of the major primaries, and would have to be up against a field of theocratic loons to attract enough support from other directions to overcome that. Again on the flip side, however, his stances would let him snatch up a chunk of Obama's base, meaning he could probably beat Obama easier than many other Republicans could.
