Muhammadu Buhari's pledge to end Boko Haram's Islamist insurgency in northeast Nigeria played a large part in his 2015 presidential election victory.With elections approaching next year and Buhari,75, having declared his intention to seek a second, four-year term, the extent to which he has done that is coming under increasing scrutiny.But as Africa's most populous nation gears up for months of hard campaigning before the vote in February 2019, the former military ruler is not just facing questions about Boko Haram.In recent months there has been a resurgence of clashes between farmers and nomadic herders - and a heavily politicised reaction - which could have an impact on polling.Ryan Cummings, Africa analyst at the Signal Risk consultancy in South Africa, noted the violence "now accounts for more civilian casualties than the Boko Haram insurgency and may continue to do so in the foreseeable future".Elsewhere, criminal violence and kidnappings for ransom in some northern states have increased, while tensions persist from pro-Biafran separatists in the southeast.Boko Haram weakened In the 12 months before the last election, Boko Haram fighters ran riot across northeast Nigeria, capturing swathes of territory with the military seemingly unable to respond.Buhari, who headed a military government in the 1980s, was seen as a better bet to end the violence, which has killed at least 20 000 since 2009.He has achieved that to an extent but persistent attacks have undermined his repeated assertion that the militants have been virtually defeated."It is fair to say that President Buhari has failed in delivering on his promise to defeat Boko Haram within his first term," said Cummings.The group recently gave a clear indication of the threat it still poses by abducting 112 schoolgirls from Dapchi in Yobe state in almost a carbon copy of the Chibok kidnapping in 2014.Buhari secured massive support across the mainly Muslim north in 2015. That looks unlikely to change significantly in 2019.In the north's biggest city and most populous state, Kano - a key election prize because of its size - people said Buhari had their vote for weakening Boko Haram.But they warned he needed to take action against security threats elsewhere."That is where he is going to face his toughest challenge," said Abdulhadi Ahmad, a garment trader. Herder-farmer violence Violence in the decades-old dispute between herders and nomadic farmers in the central states of Benue, Taraba, Nasarawa, Plateau and Kogi has flared again in the past two years.Buhari has been criticised for failing to stop the violence, which according to some estimates has killed more than 2 000 since the start of this year.It will be a key issue in central states, where the Muslim north meets the mainly Christian south, that typically swing between parties.In Benue, the head of the state's tribal leaders, Chief Edward Ujege, said Buhari "does not deserve a single vote... because he has failed to give us security".The conflict, which is driven by land and resources, has been seen largely through the prism of Nigeria's ethnic and religious identity politics.The president of the ethnic Tiv Youths Organisation, Timothy Hembaor, indicated patronage will play a part: people in Benue will back Benue's APC governor, even if he moves party, he said.Buhari "shouldn't even come here to campaign", he added. No political will Amaechi Nwokolo, from the Roman Institute of International Studies in Abuja, said Buhari, whose candidacy still needs to be endorsed by his party, had already "most likely lost the vote in Benue", an APC state."He may not win in many of the states that have gone up in flames and many people are going to use that against him around the country," added the security analyst.Ndi Kato, a campaigner for indigenous people in the central states, said the attacks put a way of life under threat and the government's lack of action had caused outrage."We feel we cannot have four more years of this," she said, adding there was "zero political will" to end the violence, which has made tens of thousands people homeless."All things being equal the Middle Belt won't be voting for this government. However, we don't know who they will be voting for - and that is another problem."* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.