Abdullah Abdullah has spent more than a decade trying to become Afghanistan’s president, contesting three separate votes and coming within touching distance in 2014 before watching the prize slip from his grasp.

In most other countries, repeated high-profile losses would almost certainly spell the end of a political career, despite Abdullah’s credentials from years serving with the anti-Soviet and anti-Taliban resistance and later in government.

In the byzantine world of Afghan politics, those battles have, however, made the urbane former ophthalmologist the most credible challenger for many who want the incumbent, Ashraf Ghani, ousted from his post in voting on Saturday.

Some of Abdullah’s team have been with him for years, others are former Ghani supporters – including one of his 2014 vice-presidential candidates – who swapped sides because of personal disputes, frustration over how he has distributed the spoils of power, or disillusionment over how he has ruled.

Facebook Twitter Pinterest An Afghan soldier stands guard in front of an election poster for Ashraf Ghani in Kabul. Photograph: Rahmat Gul/AP

Abdullah’s first election bid was in 2009, when he faced off with the then incumbent, Hamid Karzai; then in 2014 he fought two rounds with Ghani, losing in a runoff in which he claimed as many as 2m fraudulent votes were cast.

He told the Guardian that as the 2019 election approached, he was initially unsure whether to stand again, tired after years in politics.

“Until the last days before the registration deadline for candidates, I had not decided whether to run,” he said in an interview at his heavily guarded home in Kabul, dotted with reminders of his time in the anti-Taliban resistance movement under the assassinated Northern Alliance leader Ahmad Shah Massoud.

“When you fight three rounds of elections in this country, the toll it takes on your mind, body, family – the whole thing – that is not simple. I had thought that this time around someone else might do it.”

The Taliban have declared the poll illegitimate and said civilian voters should prepare to be targeted. Two deadly attacks targeting a vice-presidential candidate and an election rally have been carried out during the campaign and more violence is expected on the day despite a security deployment of more than 70,000 police, troops and intelligence officials.

Facebook Twitter Pinterest Afghan security forces personnel stop a rickshaw at a checkpoint in Jalalabad on Friday. Photograph: Noorullah Shirzada/AFP/Getty Images

Abdullah said he finally agreed to run after he was approached by the leaders of both his own Jamiat-e Islami party and other major groups. One of those is led by Gen Abdul Rashid Dostum, a warlord accused of human rights abuses, who in both 2009 and 2014 backed Abdullah’s rivals.

“I knew the difficulties of it, but I thought let’s do it again,” he said. He could be facing two gruelling campaigns: if no single candidate gets more than 50% of the vote in the first poll, Afghan law requires a second round.

Abdullah’s decision to stand again has in effect set up the vote on Saturday as a re-run of 2014’s fraud and violence plagued poll that brought the country to the brink of political collapse.

‘Voting means you’re crazy’: violence and fraud overshadow Afghanistan poll Read more

The results were so contested that the then US secretary of state, John Kerry, had to step in and negotiate a national unity government. Ghani became president, Abdullah his “CEO”, but the men spent the next five years feuding bitterly.

Now there are fears that a repeat of the 2014 dispute could result in an even graver fallout. Abdullah has ruled out another unity government. “With the same gentleman? No,” he said. Ghani has made a similar public pledge.

US diplomats have also reportedly made clear they do not want to be drawn into brokering another deal, leaving open the possibility that a festering political dispute could erupt into open conflict.

“The bad scenario is an election result that is disputed in rounds one and two, and then we do not have sufficient national and international level intervention to bring the two sides to an agreement,” said one senior Afghan source, who asked for anonymity to discuss sensitive scenarios. “This will further destabilise Afghanistan politically and could even lead to the collapse of the state.

Facebook Twitter Pinterest Abdullah campaigning in Herat on Tuesday. Photograph: Jalil Rezayee/EPA-EFE

“If a crisis in state leadership meant the US cut security and development aid, the Afghan state can’t finance itself for a couple of weeks, let alone months or years. That will make the collapse of the state inevitable, even though it is not in the interests of anyone but terrorists.”

The election is not officially a two-horse race. There are 18 candidates on the ballot paper, including the former insurgent leader Gulbuddin Hekmatyar, who until 2016 led a faction that denounced elections and periodically attacked Kabul. But three have already dissolved their campaigns and of the remaining 15 only Abdullah and Ghani are thought to be real contenders.

The presidential poll was almost postponed to allow more time for peace talks with the Taliban, but after Donald Trump used Twitter to cancel an expected US deal with the militants at the start of the month, election plans were revived and campaigning restarted. Ghani has said it is vital to give the Afghan government a democratic mandate in future talks with insurgents.

Record insecurity has already disenfranchised millions. At least a third of the country’s 7,384 polling centres will be closed for security reasons. There are also like to be more opportunities for fraud, which all sides agree is a given, although each campaign insists it will only be perpetrated by the opposition.

Facebook Twitter Pinterest Workers transport ballot boxes and electoral material to polling stations in Kandahar on Friday. Photograph: Muhammad Sadiq/EPA

The Afghanistan Analysts Network said dozens of voting stations had been declared open in areas controlled by the Taliban. “During previous polls, election material has been delivered to insecure areas … Sometimes, the material was redirected to the private houses of local strongmen and then used to stuff ballots,” the group said in an pre-election report.

New anti-corruption measures including biometric voter registration machines have been deployed to tackle fraud. But experts say campaigns may simply look for other ways to alter results, including voter intimidation and attempting to invalidate ballots cast for other candidates.

Even if anti-fraud measures work, the legitimacy of the vote may also be undermined by low turnout: the most optimistic official and campaign estimates would represent barely half the votes counted in 2014.

“In the past 18 years the nation of Afghanistan did its duty well. I voted and my family voted even in parliamentary elections,” said Rahimullah Rezai, 55, a mechanic. “But our leaders did not do their duty, and now I have lost hope.

“In this election we are expecting fraud, we are expecting explosions and there is no need to put our lives in danger to vote for Ghani or Abdullah.”

Mokhtar Amiri in Kabul contributed to this report