MOSCOW—A court in Belarus sentenced the opposition leader’s husband to 18 years in jail on Tuesday after he was arrested during an attempt to run for president against incumbent Alexander Lukashenko, a verdict his wife called political revenge. The court found Syarhei Tsikhanouski, a 43-year-old video blogger, guilty of organizing mass unrest and of inciting social hatred, and handed him one of the longest jail terms in modern Belarusian history. His supporters said the charges were fabricated and politically motivated. Syarhei, husband of opposition leader Sviatlana Tsikhanouskaya, was arrested at an opposition protest in May 2020 after being barred from taking part in an election later that year which his wife contested instead. He rose to prominence in Belarus after comparing Lukashenko, who has been in power since 1994, to a moustachioed cockroach from a children’s fairy tale. His jailing angered many Belarusians who went on to stage the biggest …