DAKAR, Senegal — When the American ambassador took up his post in Cameroon late last year, he stepped into an increasingly troubled nation, locked in battle against Islamist militants in one part of the country and armed separatists in another.

And then there is the matter of its leader.

Cameroon has not had a new president since Michael Jackson released “Thriller” in 1982.

Under the 36-year leadership of President Paul Biya, the nation has been accused of numerous human rights abuses, including killing unarmed protesters, torturing detainees, shutting off the internet and locking up journalists.

Last month, Washington’s ambassador, Peter Henry Barlerin, met with the 85-year-old president, who has taken initial steps to seek re-election in October. He told Mr. Biya that he “should be thinking about his legacy and how he wants to be remembered in the history books,” saying that George Washington and Nelson Mandela were excellent role models.