Secretary of State Brian Kemp has continuously blasted Democrat Stacey Abrams since both entered the governor's race, even as his office oversaw a complicated fraud investigation into a voter registration group founded by Abrams.

The Republican has said he's fulfilling his constitutional duty by directing his office's probe of the New Georgia Project, which last week led to a decision by the State Elections Board to refer 53 allegedly forged voter applications out of roughly 86,000 forms to the state Attorney General's office for possible prosecution.

But his critics say he should recuse himself from the probe to avoid a conflict of interest, citing his frequent attacks against Abrams as evidence he can’t be seen as a neutral arbiter of the voting complaints.

It underscores the deep animosity between the two rivals, who could wind up in a general election showdown if they survive stiff primary competition. Abrams faces former state Rep. Stacey Evans next year, while Lt. Gov. Casey Cagle and three other Republicans are competing with Kemp for the GOP nod.

Kemp and Abrams have a long-running feud over a range of elections issues, but they've clashed sharpest over Abrams' voter registration initiative, which in 2014 announced aims to register 800,000 minority voters within a decade.

It immediately earned the scrutiny of critics from both parties – as well as an eventual probe from Kemp's office. Investigators argued that tens of thousands of applications were either missing or had not been properly submitted, and over the next few years the two waged rounds of legal battles.

Abrams stepped down from the group earlier this year, but the bitter fighting between the two has only escalated. In campaign emails, Kemp has called Abrams a “radical-left Democrat” who advances an “out-of-touch, liberal agenda” with the likes of billionaire financier George Soros.

“But I’m not scared,” he wrote in one campaign fundraising email. “I took on Stacey Abrams and Soros before and I’m ready to do it again.”

And Abrams has hit back, casting Kemp as an incompetent manager of elections data while emphasizing the need for a paper trail of recorded votes and an overhaul of aging equipment.

The results of last week's investigation have added a new wrinkle in their battle. The case's lead investigator said he found no wrongdoing by the group, but raised questions about 14 people who essentially acted as independent contractors to register new voters for the program.

Her supporters say it's one thing for two competing candidates to trade fire, it's another for one of those candidates to oversee a state investigation into the rival's organization.

In a statement Monday, Abrams' spokeswoman Priyanka Mantha said Kemp is "abusing his office to target a political opponent in a desperate attempt" to deflect attention from his mishaps that include the accidental disclosure of sensitive voting data of more than 6 million Georgia voters.

Kemp campaign spokesman Ryan Mahoney said it won't apologize for his decision to oversee the investigation into what he called a “shady organization.”

"Despite pressure from left-wing radicals like Stacey Abrams, Brian Kemp is not going to recuse himself,” said Mahoney. “He's going to fight tooth and nail to keep Georgia's elections secure, accessible and fair."