A blanket primary historically allowed voters to cross party lines office by office on the same primary ballot, helping select each party's nominees. The constitutional issue begins with associational rights: people may join together around shared political beliefs, and a party has an important interest in deciding who helps choose the candidate who will speak under its name. State election rules may protect access, fairness, and orderly administration, but they cannot simply erase that party choice.

In California Democratic Party v. Jones, the Supreme Court invalidated California's state-mandated blanket nomination primary because it forced parties to let nonmembers help select their nominees. The holding does not make every broad-access election unconstitutional. A party can choose broad participation, and a state can design a system that advances candidates without claiming to select each party's standard-bearer.

A nonpartisan top-two primary uses that second design. Candidates appear together, and the two leading vote-getters advance regardless of party; the event does not purport to choose each party's nominee. Both finalists can therefore prefer the same party, and a major party can be absent from the general-election ballot. A top-two system is not proportional representation, and the word primary does not by itself make the winner a party nominee.

Participation rules can affect strategy. Closed rules encourage campaigns to identify registered partisans; open rules can make unaffiliated voters more important. Crossover voting may occur, but evidence is needed before claiming that strategic voters determined an outcome. A rule broadening access does not automatically make the electorate representative of all November voters.

The clean way to classify a rule is to ask two questions. Is the contest choosing a party nominee or merely advancing candidates? Who may participate? "Choose one party ballot without prior affiliation" points to an open primary. "Select across parties office by office, with each party's leading candidate becoming its nominee" points to the historical blanket form. "Top two advance regardless of party" points to a nonpartisan top-two system.

Video lesson: Political Campaigns: Crash Course Government and Politics #39