Confronted on Sunday with receipts that appear to prove he paid for the abortion of a woman he once dated, staunch anti-abortionist Herschel Walker – Georgia’s Republican candidate for the US Senate – had a ready response: “It’s a lie.”

Walker is competing for a Senate seat considered pivotal to determining which party controls the chamber in the 8 November midterms, but his campaign has spent weeks under fire after reports emerged earlier this month that Walker – who has publicly argued that abortion should be illegal nationwide without exceptions – sent the unnamed woman money to end her pregnancy.

In an interview with NBC News, Walker was presented with an image of a check for $700 written in 2009, to which he responded, “Yes, that’s my check.”

However, he disputed that its purpose was to pay for the termination of the woman’s pregnancy. He maintained his denial even after NBC showed him a receipt from the clinic where the woman – whose name was not revealed by the network but who has said she is also the mother of one of Walker’s children – underwent the abortion.

“It’s a lie,” Walker said, saying that it’s not unusual he would send money to someone with whom he had a child. “I know that’s what the people want to know – it’s a lie.”

Walker also said he has helped the woman “forever” and had “no idea” what the $700 might have been for.

“So when they show me a check and I never said anything about an abortion, I never said anything about anything and they say this, that’s just people talking,” he added.

A former college football and NFL star who is endorsed by former president Donald Trump, Walker is trying to unseat Democratic incumbent Raphael Warnock, who won a Senate seat just last year in a special election and is now vying for a full six-year term. Georgia, where early voting began on Monday, is among a handful of states including Pennsylvania, Wisconsin and Arizona which are expected to determine whether Democrats maintain control of Congress’s upper chamber or lose power to the GOP.

The senior pastor of Atlanta’s Ebenezer Baptist church where Martin Luther King Jr once preached, Warnock has held off on attacking Walker over the abortion revelations, but voters appear to have taken note.

Poll aggregator FiveThirtyEight registered a significant jump in Warnock’s chances and a decline in Walker’s prospects in early October, when the Daily Beast broke the abortion story.

At their lone debate encounter on Friday, Walker attacked Warnock for being soft on crime and for supporting Democratic policies he claimed drove inflation higher. But the Republican also denied ever supporting a hardline abortion ban and created an unusual scene by pulling out a badge to prove his support for law enforcement – even though he was never known to have served as a police officer.

Asked to clarify the moment by NBC, Walker again displayed the badge, describing it as both “a real badge” and an “honorary badge” that he always carries with him.

He said it was given to him by the sheriff of Georgia’s Johnson county, where his home town is located. The former running back for the University of Georgia Bulldogs added: “If anything happens in this county, I have the right to work with the police in getting things done.”

NBC reported that the sheriff of Johnson county, a rural area about 150 miles south-east of Atlanta, confirmed that he had given Walker the badge and could call upon him if there were a crisis.

The 8 November midterms are 22 days away, but Walker and Warnock’s Friday debate appearance will be their only encounter of this campaign.

While Warnock has committed to three debate appearances, Walker would only participate in the one. Warnock appeared at a Sunday debate against libertarian Senate candidate Chase Oliver hosted by the Atlanta Press Club, where Walker’s absence was noted with an empty lectern.