Around the beginning of his rule, Tar-Calion the Golden was a dear friend to Amandil the Lord of Andúnië, despite Amandil being leader of the Faithful, and he let him be a member of the Council of Númenor. Obviously, at the beginning of his rule Tar-Calion has been more tolerant towards the Faithful than the Kings from Tar-Herunúmen to Tar-Telemnar.
In 3261, he captured Sauron who eventually grew to influence in Númenor and persuaded Tar-Calion to commit human sacrifices for Melkor, to hate the elves and Faithful even more than his predecessors and eventually to attack Valinor.
Why and at what occasion did Tar-Calion listen to Sauron while he was still a mere prisoner of the King, and why did he let himself influence that much by Sauron's evil whispers? Shouldn't Tar-Calion have known better? Why didn't he just let Sauron be executed?