If Sen. Russ Fulcher upsets Gov. Butch Otter in the May 20 Republican primary by a hair's-breadth, he may credit his effort to convince non-Republicans to re-register and vote for him over Otter.
But the result of the Meridian lawmaker's open courtship of Democrats, Libertarians and Constitution Party members appears quite modest.
"It was a tepid response," said Secretary of State Ben Ysursa, Idaho's top election official and a co-chairman of the Otter campaign.
All four parties made slight gains before last month's re-registration deadline. In order to vote Republican, voters who had registered in one of the three other parties had to switch by March 14 to vote Republican in May; other voters can choose their ballot when they vote.
With Fulcher's effort and a busy GOP primary at the top of the ticket, Republicans had the largest proportional gain.
The increase of 1,630 registrants, however, would be decisive only in a close race. The new Republicans equal less than two-tenths of 1 percent of Idaho's 742,742 registered voters and 1 percent of the number of people who cast ballots in the 2010 GOP primary. Otter won that seven-way contest by 47,000 votes.
Fulcher made his pitch the first week of March, but he wasn't alone.
In late February, Otter alerted people to the re-registration deadline, though he said he wasn't trying to turn Democrats. An unusually competitive race between 2nd District GOP Rep. Mike Simpson - who has done well historically in Democratic precincts - and tea party challenger Bryan Smith also likely lured voters to the GOP.
What appears more promising for GOP candidates is drawing from the largest voter pool - the 59 percent who remain unaffiliated. Those 437,962 voters have the option of declaring themselves Republicans when they vote, either absentee or on Election Day, as do newly registered voters. The first absentee ballots were mailed Friday and early in-person voting begins April 28 in Ada County.
The number of registered Republicans rose from 240,996 on March 1 to 242,626 on April 1. The proportion of Republicans among all 742,742 registered voters rose from 32.495 percent in March to 32.666 percent in April. That represents the gain of 1,630 voters, or 0.171 percent.
Democratic registrations rose by 180 to 56,921, raising their percentage of all voters from 7.651 percent in March to 7.663 percent in April, an increase of .012 percent.
Libertarian registration rose by 62 to 3,488, up from .0046 percent to .0047 percent. Constitution registration gained 32 to 1,745, staying flat at .0023 percent.
The largest shift came from unaffiliated voters joining parties. In March, unaffiliated voters accounted for 438,750 of the 741,621 registered, or 59.161 percent. In April, that group fell to 437,962, or 58.966 percent, down 0.195 percent.
Comparing Jan. 1 to April 1 shows the modest shift to party registration began before Otter and Fulcher started talking openly. On Jan. 1, 59.266 percent were unaffiliated; 32.417 percent GOP, 7.632 Democrat; 0.457 percent Libertarian Party and .227 percent Constitution.
Dan Popkey: 377-6438, Twitter: @IDS_politics