What? they can do that if the candidate had enough signatures or whatever they go through to get on the ballot?
Well I don't know how interesting this topic is, it's just kind of an aside as to why I can talk up 3rd parties more than I can actually vote for them. But with the California open primary system (and maybe any state that in the future decides to adopt open primaries - Oregon was considering it I think, so this might be of interest to Oregonians) while all candidates are on the primary ballot only the top two candidates get on the general ballot. The top two candidates are sometimes unsurprisingly a Democrat versus a Republican. But often the top two candidates are both Democrats and so there isn't any Republican candidate in the general election at all (it's a pretty blue state ok - a red state with these rules might be the reverse). It very rarely includes a 3rd party candidate, though in theory and occasionally in practice it does, if they places 1st or 2nd in the primary. Whereas before open primaries, the top contender for every party that is approved in the state, major and minor parties, was on the general election ballot.