The proposal is to open the primaries to everyone, and then the two candidates who receive the most votes, regardless of party, will appear on the final election ballot. This means that in the final race the votes could be limited to just choosing between a Republican and a Democrat, or they could be limited to just choosing between two Republicans or between two Democrats.
CAIVP assures the voters that third parties will not be negatively impacted.
How will Top Two Candidates Open Primary impact third party candidates?
The Top Two Open Primary will level the playing field for third parties by allowing them to appeal to broader base of voters in the primary. Under the current election system, third parties have an extremely difficult time winning legislative, congressional and statewide elections. Only one third party candidate has served in the state legislature in modern California history. Under a Top Two Open Primary system, for example, a general election could conceivably pit a Democrat against a Green party candidate in San Francisco or a Republican and Libertarian candidate against each other in Orange County.
It is bad enough that this attacks free association, as the individuals in political parties have a right to say who they are and are not associated with, but the position put forth by CAIVP stands in stark contrast to reports by third parties in states where "top two" has been implemented. The effect has been to shut out Greens and Libertarians in the state of Washington except in races where there was no major party opposition to major party incumbents.
Even when someone claiming association with a third party did make it to the November ballot (as in the cases where there was no major party opposition) there really is a "purity of message" issue. A hard core libertarian could claim "Green" and thus dilute the message of the Green Party, and a hard core green could claim "Libertarian" and thus dilute the message of the Libertarian Party. It is bad enough that Libertarians have to deal with the No True Libertarian argument as well as other baseless accusations, this would truly make it impossible for third and minor parties to get their message out.
If reform is the goal, try attacking the obstacles to ballot access instead, or try attacking safe districts or campaign finance limits. Phony reform is not what is needed.