National Rifle Association headquarters in Fairfax, Virginia/Photo courtesy of Nicole S Glass/Shutterstock.com

An NRA-endorsed candidate for agriculture commissioner is “retooling” an ad after the gun-rights group said he made a “mistake” in assigning a failing grade to a primary opponent.

Marion Hammer, the National Rifle Association's longtime Florida lobbyist, requested that the endorsed candidate, Matt Caldwell, apologize for the ad against Republican primary opponent Denise Grimsley.

Despite Hammer's request, Caldwell, a state House member from North Fort Myers, issued a statement that adopted a less-conciliatory tone and continued to pound Grimsley's gun-rights voting record.

Caldwell's campaign recently sent out a print ad that assigned to Grimsley a “D” grade for 2016 that appeared to be from the NRA. But the gun-rights group, which grades candidates on how they vote on Second Amendment issues, actually gave Grimsley, a state senator from Sebring, a grade of “B” that year, according to Hammer.

The ad and Monday's statement from Caldwell drew rebukes from Grimsley's campaign. Hammer repeatedly described the ad copy as a “mistake.”

“It's clearly a mistake,” Hammer said. “And I would certainly hope that Matt Caldwell, the candidate we have endorsed, would admit that it was a mistake and apologize to her and move on. That's the professional thing to do.”

Hammer declined to comment further after Caldwell issued a statement that continued to question Grimsley's record on gun issues.

“In order to avoid confusion, I asked my team to retool the ad this weekend, but we will not back down from the clear contrast between ourselves and our opponents when it comes to defending the Second Amendment,” Caldwell said in the statement.

The disputed ad asks voters: “Who can you trust to protect your Second Amendment rights?” It then lists grades that Caldwell and Grimsley purportedly received from the NRA in 2016 and a failing mark that former lawmaker Baxter Troutman, another candidate for agriculture commissioner, received from the organization in 2008.

In responding to Hammer's statement, Caldwell said: “It is common knowledge that Sen. Grimsley has received less than an A-rating from the NRA multiple times throughout her legislative career.”

“A simple Google search reveals that she partnered with disgraced Sen. Jack Latvala to vote against a pro-gun bill in 2014,” Caldwell said, referring to a former Clearwater lawmaker who resigned after a sexual-harassment investigation. “Additionally, ProjectVoteSmart.org lists Grimsley as having a 64 percent grade from the NRA in 2016.”

Grimsley campaign spokeswoman Sarah Bascom said that while Hammer repeatedly called the recent ad copy a “mistake,” Caldwell's campaign has “been pushing this false attack for months and finally got busted.”

“Is Matt Caldwell admitting that his campaign knowingly lied in an ad he approved?” Bascom said. “Mudslinging is not a good look, but it usually means someone knows they are losing.”

High grades from the NRA are often coveted by Republican candidates. Under the NRA grading, a “B” signifies a lawmaker who “may have opposed some piece of pro-gun reform or supported some restrictive legislation in the past,” but is otherwise generally pro-gun.

A “D” advises NRA members that the candidate is “anti-gun” and “usually supports restrictive gun control legislation and opposes pro-gun reforms” and “can usually be counted on to vote wrong on key issues.”

Caldwell received an “A” grade in 2016 and an “A plus” for the current year.

An “A plus” grade goes to candidates who have “an excellent voting record on all critical NRA issues” and who have offered a “vigorous” defense of the Second Amendment. Grimsley received a “B plus” for the current year.

Grimsley's marks have been attributed to her vote in 2014 on an amendment to a bill allowing people without concealed-weapons licenses to carry guns during declared emergencies.

Jim Turner and Dara Kam report for the News Service of Florida.