President Yoweri Museveni displays his inked finger after casting his vote during presidential elections on 18 February. Photograph: James Akena/Reuters

Yoweri Museveni has had a good run. Having seized power in Uganda in 1986, he has held the presidency ever since. As guerrilla leader turned politician-statesman, Museveni fitted the late 20th-century leadership profile that predominated in post-colonial Africa. Where once the heinous dictatorship of Idi Amin held sway, the Museveni era brought a democratic reformation. Where once chaos reigned, his strong grip on the fledgling state brought stability and, for many Ugandans, a degree of economic security and gradual social progress.

It is a pity Museveni is jeopardising all that now. By grabbing at a fifth consecutive term at the age of 71, while security forces simultaneously oppress his rivals, beat their supporters and disrupt voting, he risks tarnishing a legacy of achievement that, though modest, might have ensured him a respected place in Uganda’s history. He just cannot let go of power, it seems. He may thus come to be remembered for less creditable reasons.

The disconnect between Uganda’s past and present is obvious. The average age of the country’s 38 million people is 15. Most Ugandans were not even born when Museveni took office. The priorities of this electorate include jobs, education, free speech and open debate, an end to corruption and engagement with the world. They barely know the old man in the State House. His outlook and prejudices, including his notorious anti-gay record, belong to another age. These new citizens take the stability he established for granted, while increasingly balking at the means used to maintain it.

Kizza Besigye, who apparently came second to Museveni in last week’s presidential election, was briefly arrested shortly before the vote. He has already promised a campaign of “defiance” if, as seems certain, he deems the polls not free and fair. Opposition rallies have been disrupted, social media shut down and independent news organisations intimidated and harassed. There appear to have been serious irregularities in the opposition strongholds of Kampala and Wakiso, where voting was delayed or did not proceed at all. On Friday, police raided Besigye’s party headquarters, detaining him again for specious reasons.

Uganda has been here before. Protests after the previous presidential election in 2011 produced a violent security crackdown. Given the apparent margin of the president’s victory, stemming from his traditional, strong support in rural areas where 80% of Ugandans live, and given the extensive state security apparatus – 150,000 military, police and auxiliaries were deployed during the polls – it seems unlikely at this stage that Uganda will suffer the sort of lethal meltdown witnessed in nearby Burundi after elections last year. Besigye and the other leading opposition candidate, Amama Mbabazi, a former prime minister sacked by Museveni, will certainly strive to avoid the sort of extreme divisions seen in South Sudan.

But if the situation deteriorates, and given Museveni’s high-handedness, it is possible that Uganda will face the sort of long-running, damaging post-election instability seen in neighbouring Kenya in 2007 and 2013. Addressing a rally in eastern Uganda last month, Besigye indicated his Forum for Democratic Change party would continue to challenge what he characterised as a complacent, corrupt presidency for life. Besigye lampooned Museveni’s famous slogan celebrating Uganda’s steady progress. “I have not met someone as cynical as Museveni,” he said. “This massive poverty all over the country, he calls it ‘steady progress’. When you go to a hospital and there are no drugs, ‘steady progress’. All the roads are bad, ‘steady progress’.” As Kenyans might testify, making a mockery of a humourless hardman such as Museveni, a latter-day Daniel arap Moi, is a dangerous game.

Museveni’s clinging to power would not matter so much if he were offering a fresh programme mapping Uganda’s road ahead. Instead, he offers more of the same. By dismissing Mbabazi, a respected party technocrat once seen as his heir, he squandered the chance of an orderly transition within the ruling National Resistance Movement. By failing to quash suspicions that he may promote his wife, Janet, or son, Muhoozi Kainerugaba, as successor, he risks accusations of dynasty politics like the Mugabes in Zimbabwe (or the Bushes and Clintons). Like another eternal president, Paul Kagame in next-door Rwanda, Museveni sets a poor example for African democracy and governance. By obstructing Uganda’s changing needs and aspirations with his grimly immovable presence, he does the nation a disservice.