A Turkish court sentenced Istanbul Mayor Ekrem Imamoglu to jail on Wednesday and imposed a political ban on the opposition politician who is seen as a strong potential challenger to President Tayyip Erdogan in elections next year.  Imamoglu was sentenced to two years and seven months in prison along with the ban, both of which must be confirmed by an appeals court, for insulting public officials in a speech he made after he won Istanbul's municipal election in 2019.  Ahead of the verdict, a few thousand Imamoglu supporters rallied outside the municipality headquarters on the European side of the city after Imamoglu called on Twitter for them to gather. "Truth, law, justice," they chanted.  Across the Bosphorus on the Asian side of the city of 17 million people, riot police were stationed outside the courthouse, although Imamoglu continued to work as usual, dismissing the court proceedings.  "Such a handful of people cannot take the authority given by the people. Our struggle is beginning to get even stronger, with God's permission," Imamoglu said in a brief video shared on a principality website.  The ruling comes just six months ahead of scheduled presidential and parliamentary elections, in which Imamoglu has been mooted as a possible leading challenger to Erdogan. A main opposition presidential candidate has not yet been chosen.  ‘Fools’  Imamoglu, from the opposition Republican People's Party (CHP), was tried over a speech after Istanbul elections when he said those who annulled the initial vote - in which he narrowly defeated a candidate from Erdogan's AK Party - were "fools".  Imamoglu says that remark was a response to Interior Minister Suleyman Soylu for using the same language against him.  After the initial results were annulled, he won the re-run vote comfortably, ending the 25-year rule in Türkiye’s largest city by the AKP and its Islamist predecessors.  The outcome of next year's elections is seen hinging on the ability of the CHP and others in opposition to join forces around a single candidate to challenge Erdogan and the AKP, which has governed Türkiye for two decades.  A jail sentence or political ban would need to be upheld in appeals courts, potentially extending an outcome to the case beyond the election due by June.  Critics say Turkish courts bend to Erdogan's will. The government says the judiciary is independent.  "The ruling will be final only after the higher court decides whether to uphold the ruling or not. Under these circumstances, it would be wrong to say that the political ban is in place," Timucin Koprulu, professor of criminal law at Atilim University in Ankara, told Reuters after the ruling.  Sezgin Tanrıkulu, a CHP MP, said the court decision was "political rather than lawful".