Sen. Ted Cruz got a surprise win after a poll released Monday that found Donald Trump leading with the support of 30 percent of Idaho Republican voters in the competition for 32 delegates. Cruz was second in the poll with 19 percent and Florida Sen. Marco Rubio had 16 percent.
The primary was open only to Republican registered voters, but residents could change their registration to the GOP at polling places on Tuesday.
All 13 candidates from the original GOP field were on the ballot.
State lawmakers moved their primary date up from May in 2012 to March this year to give voters a more important role in the presidential campaign.
Idaho Democrats will hold their caucuses on March 22.
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