Beginning in 2011, a law went into effect that restricts an elector to voting only in the primary election of the political party for which he or she is registered, unless a party notified the Secretary of State in writing that the political party elects to allow additional voters (unaffiliated voters and/or voters registered with another party) to participate in the party's primary election. (See Idaho Code § 34-904A.)
The purpose of primary elections in the State of Idaho is to allow members of a recognized political party to select that party’s nominees to go on the general election ballot. Primary elections often are referred to as “party primaries”.
As a result of a federal court decision in Idaho Republican Party v. Ysursa, the 2011 Idaho Legislature passed House Bill 351 implementing a closed primary system. Persons who are not members of a party may not participate in the selection of that party’s nominees. However, Idaho law does allow the political parties the option of opening their primary elections to “unaffiliated” voters and members of other political parties if they so choose. The party chairman must notify the Secretary of State 6 months prior to the primary if the party intends to open it's primary election to those outside the party.
So in primary elections, unless the party chooses to allow others outside the party to participate in its primary election, only registered voters of a political party may vote to select their party’s nominees. In other words, at primary elections, registered Republicans may vote only for Republican candidates, and registered Democrats may vote only for Democratic candidates. Persons who are registered as “unaffiliated” (meaning not affiliated with any political party) may not vote for partisan candidates in primary elections unless the party decides to allow them. However, an unaffiliated voter may affiliate with a party up to or on Election Day and vote in that party's election. Independent candidates appear on the ballot only at the general election.
Electors can designate their party affiliation with the Democratic, Republican, Constitution or Libertarian Party or select no party affiliation (Unaffiliated) in any of the following ways:
There are elections on nonpartisan issues scheduled to be held in conjunction with primaries, such as judicial elections, bond or levy elections or possibly state or local question elections. All registered voters are entitled to vote on nonpartisan issues during primaries.
Party registration requirements have no effect on general election procedures. At general elections, all voters receive exactly the same ballot and may vote for any candidate whose name appears on it, without regard to the political affiliation of the candidate or the voter.
For a primary election, an elector may change their political party affiliation or become “unaffiliated” by filing a signed form with the county clerk no later than the 10th Friday prior to such primary election, as provided for in Idaho Code § 34-704.
An “unaffiliated” elector may affiliate with the party of the elector's choice by filing a signed form up to and including election day. The application form for an absentee ballot described in Idaho Code § 34-1002, may also be used for this purpose.
An “unaffiliated” elector may affiliate with the party of the elector's choice on or before election day, by declaring such political party affiliation to the poll worker. The poll worker shall then record in the poll book the elector's choice. After the primary election, the county clerk shall record the party affiliation so recorded in the poll book as part of such elector's record within the voter registration system as provided for in Idaho Code § 34-437A.