What is a closed primary and what does it mean for voters?

A “Vote Here” sign directs voters to the polling location for Precincts 3040 and 3034 at the Scottish Rite Masonic Center in Lake Worth Tuesday, March 15, 2016. (Bruce R. Bennett / The Palm Beach Post)

A “Vote Here” sign directs voters to the polling location for Precincts 3040 and 3034 at the Scottish Rite Masonic Center in Lake Worth Tuesday, March 15, 2016. (Bruce R. Bennett / The Palm Beach Post)

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Why? Multiple states, including Florida, Nevada, New York, Maine, Michigan and Pennsylvania, hold closed-primaries, meaning those who are not registered as Democrat or Republican aren’t able to weigh in on the primary.

In Palm Beach County, Florida, elections supervisor Susan Bucher reported dozens of people had tried to vote in the primaries but were unable to because of their registered party affiliation, “and they’re really mad.”

“Traditionally they haven’t voted in primaries,” Bucher added.

Florida law requires voters to be party affiliated at least 29 days in advance of a primary. That was by Feb. 16, Bucher said.

In total, 28 states -- plus the District of Columbia -- have closed presidential primaries and caucuses. In some states, only one party holds a closed presidential primary: in Alabama, Democrats; and in Oklahoma, Idaho, South Dakota and Utah, Republicans.

More than 20 states hold what are known as open presidential primaries, meaning a registered voter can vote in any primary, regardless of party affiliation. A handful of states also hold a hybrid presidential primary.