Tunisians were on Sunday casting their ballots in a presidential election that the opposition says is marred by a lack of credibility and integrity. The polls are pitting incumbent President Kais Saied against only two rivals, one of whom is imprisoned. Serious challengers to Saied, who is seeking a second term in office, have been excluded. Earlier this week, a Tunisian court confirmed a 20-month prison sentence for presidential contender Ayachi Zammel, a businessman and a liberal politician, on charges of falsifying electoral endorsements. The ruling will not affect Zammel’s candidacy. The t…