Having repeatedly threatened to kill opposition leader Bobi Wine, who says the vote was rigged and is in hiding, Kainerugaba boasted on Friday that 30 "terrorists" from Wine's party had been killed and 2,000 "hooligans" arrested. There was no immediate response from the party.
In the run-up to the vote, security forces disrupted opposition rallies, detaining supporters and sometimes opening fire.
Adding to accounts from a business source and a security official, Andrew Mwenda, a close adviser to Kainerugaba, told Reuters he had played a critical role in the four-day internet blackout, saying it was to prevent any sabotage.
Kainerugaba personally mobilised the police and army to target "roughnecks and ruffians" supporting the opposition National Unity Platform party led by popstar-turned-politician Wine, Mwenda added.
"He's number one in security in this country," Mwenda said.
Kainerugaba could not be reached and spokespeople for the government, military and presidency did not respond to requests for comment on the internet blackout, crackdown or succession plans.
'TIRED OF WAITING' FOR POWER
Kainerugaba, who attended Britain's prestigious Sandhurst military academy and is an admirer of Mao Zedong and Fidel Castro, first announced in 2023 that he wanted to be president after his father, saying he was "tired of waiting forever".
Since then, he has sidelined critics within the ruling party and military, retiring rival officers and boosting pay to secure soldiers' loyalty.
Museveni has never commented in public about who will follow him, beyond saying his party will make the decision.
Though Kainerugaba's presidential ambitions have previously sparked concern in Museveni's inner circle, his role in securing the election victory has strengthened his position, the security official and business source said.
A handover from father to son would not be without risks of a backlash in the East African country, which has a $65 billion economy and enjoyed decades of stability under Museveni.
Kainerugaba does not speak to journalists and has a reputation for late-night social media posts – including threats to behead Wine and castrate another opposition leader in 2025 and invade Kenya in October 2022.
Both he and his father apologised for the threat to a neighbouring nation, and Kainerugaba has said some of his posts are meant to be ironic.

His erratic style has displeased some in the older generation of Uganda's political and military elite.
But his position as security czar and prospective future leader looks stronger than ever, according to five people with close knowledge of the matter, two of whom are involved in talks about the transition.

"At this point, it's hard to think of anyone outside the family who could challenge him," said Kristof Titeca, a Uganda expert and professor at the University of Antwerp.
Kainerugaba grew up in exile in Tanzania, Kenya and Sweden before his father took office in 1986. He returned home to lead the Special Forces Command, an elite unit often described as an army within the army.

His swift rise and frequent interjections in politics have drawn some criticism but seldom serious sanction.
"There (are) people who are in the military who are not happy with General Muhoozi's behaviour ... either expressing interest in the presidency for himself or praising his father or insulting his father's rivals," said Frederick Golooba-Mutebi, a Ugandan researcher and analyst.

"It would seem as if there are laws that apply to other military officers, but those laws don't apply to the president's son."
In 2022, Museveni and his younger brother Salim Saleh, who serves as a special presidential adviser, did warn Kainerugaba about his posts, two business sources told Reuters, citing family members. Saleh did not reply to a request for comment.

CALMER IN PERSON?
Despite his intimidating public profile, three sources who have met Kainerugaba say he is thoughtful and strategic in person. "When you talk to him outside the confines of Twitter, he is a different person," said political commentator Charles Onyango-Obbo.
Mwenda said most of Kainerugaba's incendiary posts were in fact jokes. Kainerugaba enjoyed "a glass or two of whisky" but did not abuse alcohol, he added.
If Museveni dies in office, the vice president is meant to take over temporarily and hold an election. Saleh is expected to play a kingmaker role on behalf of the family, several sources told Reuters.

"Nobody is safe in Uganda ... in a country where a military general will consume their whisky and wish somebody death," Wine told Reuters this week from an unknown location, in a clear allusion to Museveni's son.

Veteran ruling party politicians have made no secret of their disquiet over the prospect of a Kainerugaba takeover, but their influence is waning.
All but two members of the ruling National Resistance Movement's 14-member central executive committee were replaced last year, and current members are more broadly supportive of Kainerugaba, said academic Titeca.

Kainerugaba has overseen increases in salaries of rank-and-file soldiers, in some cases by over 300%, while also personally announcing promotions and retirements and launching an anti-corruption drive.

Kainerugaba's strong relationship with Rwanda's President Paul Kagame, whom he refers to as "Uncle Paul", has fuelled speculation that he might ask Kagame for help should he be challenged, according to sources.
Mwenda said the friendship went back decades and was clearly an advantage. "If I was asked for an ally, he (Kagame) is the first person I would go to." A spokesperson for Rwanda's government did not respond to requests for comment.

On the streets of Uganda, where the average national age is just 16, many condemn the idea of a family handover.
"Uganda is not a kingdom, we won't allow it. If they think they can put the son in place of the father they are wrong," 23-year-old Fahad said in the capital Kampala.
Reporting by Ammu Kannampilly; Editing by David Lewis and Alexandra Hudson
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