It was unclear who commissioned the poll —National Research Inc. did not respond to multiple inquiries seeking clarification — but both Kelly's campaign and the National Republican Congressional Committee said they were not involved. National Research has in the past conducted polls for other Arizona Republicans, the NRCC and various conservative PACs.

The firm released the poll the day before the primary for the special election to finish Giffords’s term. The three-term congresswoman stepped down in January, about a year after being critically wounded in a shooting spree that also injured Barber. The former district director for Giffords, Barber has said he also plans to run in a regular election in the fall for the regular term starting in January 2013.

Antenori, a state senator, is the only Republican in the race who has held elected office. But Antenori’s fundraising has been lackluster and he fired his campaign treasurer last week after reports filed with the Federal Election Commission were deficient and out of compliance.

National Research only polled 300 likely special-election voters in Arizona, leading to a higher-than-normal margin of error of plus or minus 5.7 percentage points. The poll was conducted on April 12.

- This post was updated at 11:44 a.m. to correct that Kelly's campaign said it did not commission the poll.