To his enemies, Martin McGuinness is an unrepentant former terrorist with innocent blood on his hands. After all, as a young man in Northern Ireland he served as a commander with the Irish Republican Army during the 30 anguished years of the Troubles, the sectarian struggle that cost the lives of more than 3,500 people.

But it’s a past that voters in the Irish Republic were invited to ignore when they went to the polls today to elect a new president. At 61, McGuinness is seeking to complete a remarkable political journey by standing as the candidate of Sinn Féin, the political wing of the republican movement that wants a united Ireland.

And if McGuinness’s chances of victory are slim, polls suggest that he can expect to take a substantial share of the vote, thanks not only to his successful reinvention as a democratic politician but also to some last-minute revelations from Sinn Fein about the questionable past of the frontrunning contender, businessman Sean Gallagher.

The campaign has not been easy. McGuinness’s role in the IRA is undisputed, and still shocking to many who believe that his violent background should disqualify him from serving as head of state. In 1973, he was jailed in Ireland for six months after being found in a car carrying 250 pounds of explosives and 5,000 rounds of ammunition.

It’s known, too, that as a 21-year-old he was the organization’s local leader in his native Derry at the time of the Bloody Sunday massacre of 1972, when British soldiers shot dead 14 demonstrators. There are suggestions, too, that he ordered terrorist killings, and he’s been challenged on the trail by angry relatives of IRA victims.

The seven-year post of president is largely ceremonial, but the role does carry powerful symbolic significance, and the Irish Environment Minister Phil Hogan has warned that electing McGuinness would do “irreparable harm” to the country’s international image and leave Ireland looking like “a banana republic.”

In response, McGuinness has claimed—to much skepticism—that he quit the IRA in 1974 to pursue a political solution through Sinn Féin and that his “struggle” was against “the armed forces of the [British] state.” In one recent interview, he said, "I am putting myself forward as someone who has made an immense contribution to peace in Ireland.”

Certainly, his achievements in helping to negotiate the Good Friday peace agreement of 1998 that brought the Troubles to an end will have counted in his favor. So, too, will his success as an efficient member of the power-sharing government of Northern Ireland in which he serves as deputy first minister. (A citizen of Northern Ireland, McGuinness can stand for election in the Republic).

His charm has even helped to win the grudging respect or even friendship of one-time sworn adversaries. Converts are said to include the Rev. Ian Paisley, the firebrand former leader of the Democratic Unionist Party, the largest of the Protestant parties in Northern Ireland that favor continued union with Britain, and now a partner with Sinn Féin in government.

Still, he’s found it hard to make much headway in the presidential race, which has been consistently led by Gallagher, an independent who made his name as an entrepreneur and TV personality. Labour politician Michael Higgins is in second place. Some polls suggested that McGuinness might win less than 15 percent of the vote.

But that was before the damaging claim from McGuinness in a live television debate earlier this week that Gallagher had acted as a “bagman” for Fianna Fáil, the hugely discredited political party, almost universally blamed for the sleaze and economic mismanagement that led to Ireland’s current slump.

Gallagher was obliged to admit that he might have collected an envelope containing a €5,000 donation from a convicted fuel smuggler for the former Fianna Fáil leader and prime minister Brian Cowen.

How many of Gallagher’s supporters may have switched their support to McGuinness won’t be known until the final result is announced on Saturday. What’s already clear is that a questionable past is no absolute bar to a political future in Ireland.