Two of the most respected republican families in McGuinness's native city say they're disgusted that he has "disowned" IRA members who laid down their lives for the republican cause.
Martina Duffy, whose IRA father Patsy died in a hail of SAS bullets, said: "Martin McGuinness has abandoned the IRA and criminalised its members as he desperately tries to woo Southern voters in the presidential election.
"He says the Irish Army is the only Oglaigh na hEireann he supports. It's a pity, he didn't tell that years ago to the dozens of volunteers in another Oglaigh na hEireann who now lie dead in Derry city cemetery.
"They're in their graves while he wants to live in luxury in Aras an Uachtarain."
Duffy claimed IRA families in McGuinness's own republican heartland in Derry were horrified at the "u-turns" he was doing during the election campaign.
She said McGuinness had "criminalised" her father and other IRA martyrs in a desperate attempt to get elected. "He should hang his head in shame for what he's done," she added.
Patsy Duffy (50) was shot dead by the SAS in 1978 as he checked an arms' dump in a house in the Brandywell. "The SAS fired 36 bullets at him. He was shot in the back and the side. He was unarmed but our family never complained because, as an IRA volunteer, he knew the risks involved," his daughter said.
Her father's jacket, shirt, cardigan and trousers were riddled with bullet holes. Duffy washed the blood out of them but refused to part with the clothes. Today, they are lovingly stored in her Derry home. "I keep them to remind me what daddy went through for the IRA," she said.
She told the Sunday World how McGuinness had attended her father's wake and funeral. "He told us he was proud of IRA men like my daddy. He saw the Oglaigh na hEireann my father fought and died for as the one and only Oglaigh na hEireann. He didn't even recognise, let alone, respect the Free State Army.
"Now he's swearing allegiance to them and singing their praises. He's got 40 faces – a different one for everybody he meets." And Martina Duffy added: "Martin McGuinness has told voters he's ashamed of some IRA actions and thinks they were murder.
"Well, genuine republicans in Derry are ashamed of him. He's portraying himself as Ireland's Nelson Mandela. He says he's a man of peace and always was. Who does he think he's kidding? It's a joke, a sick joke."
Accusing McGuinness of treachery, Duffy said: "For decades, he stood at the republican monument in Derry city cemetery giving orations as IRA men were buried and vowing the war would go on until there was a united Ireland.
"Hundreds of young men and women in this city believed him and ended up in graves themselves or the lucky ones were jailed. And those prisoners came out to wrecked marriages, children who grew up not knowing them, no jobs and no chance of a job.
"McGuinness has left us to cope with the wreckage of the war while he pursues power and position. All he's out for is himself."
Duffy's mother struggled to cope after her husband's death: "Mammy was left to rear six wee children on her own. I'm glad she's dead now because it would have broken her heart to see Martin McGuinness do a u-turn and criminalise his old comrades.
"It's not just IRA victims who are furious at McGuinness – republicans like my family are just as angry." Duffy denounced the Sinn Féin presidential candidate for saying he'd meet Prince Charles, commander-in-chief of the parachute regiment which killed 14 civilians on Bloody Sunday. "It's like a bad dream," she said.
She added that she now respected John Hume far more than McGuinness: "People, including my mother, protested outside John Hume's house years ago for saying a lot less anti-republican things than Martin McGuinness has since said.
"John Hume is a man of principle. I don't agree with his politics but he stayed true to himself and his beliefs – he didn't change them when it became opportune."
Danny McBrearty, whose IRA brother George was killed in May 1981 by the SAS in Derry, said: "Martin McGuinness was at George's funeral and wake. Had he said then that my brother was wrong and that the IRA wasn't Oglaigh na hEireann, he'd have been thrown out of our house."
George McBrearty is widely regarded as being one of the IRA's most active members in Derry. He was responsible for killing several RUC men and British soldiers. "Martin McGuinness knew George very well army-wise," said Danny McBrearty.
"He was fully aware of what George was capable of and he didn't have a problem with it. Yet now he's turning his back on men like my brother. George was 24-years-old when he was killed. He left behind three children – the youngest was only three weeks old.
"Republican families like ours are now asking what it was all for not just in terms of our own loss and sacrifice but on what we inflicted on our enemy. More than 3,500 people died in the war. As republicans, we thought we were fighting for Irish freedom. We certainly weren't fighting to make Martin McGuinness head of the 26-county state."
Danny McBrearty – himself jailed in Ireland, Britain and the US on IRA charges – has known McGuinness for over 40 years: "We worked together as young lads in Doherty's butchers' shop on the Strand Road.
"We were in the IRA together in the 1970s. We were very close. I always thought of Martin as a sound army man, totally committed to the struggle. Never in a million years did I think he'd end up where he is today. He's a constitutional nationalist, not a republican now."
McBrearty added: "People went to hell and back for the IRA in this city. Martin has turned his back on all that and he's even trying to rewrite history and pretend he wasn't part of it. The families of dead volunteers in Belfast, Tyrone and all over the North are very disillusioned at what's happened. They feel hurt and abandoned."
The Sinn Féin candidate has refused to rule out wearing a poppy on Remembrance Sunday if he's elected President. "You wont find any republicans in Derry doing the same," McBrearty said. "For us, the poppy isn't a neutral symbol to honour the dead. It is, and always will be, a symbol of British oppression."
The ex-IRA man said he personally knew no former comrades who supported McGuinness's presidential bid. "The only ones backing it are MLAs and others who have well-paid positions in Sinn Féin or who belong to the party's middle-management. The ordinary volunteers who put their lives on the line and fought the war are appalled."