Many of Mr. Khatami’s allies, including Mr. Karbaschi, were jailed during the eight years that he was in office. Former supporters say Mr. Khatami failed to help them, while Mr. Karroubi, who was then the speaker of Parliament, backed them more strongly. Emadedin Baghi, a human rights advocate and journalist who once supported Mr. Khatami, said he would vote for Mr. Karroubi this time. “Mr. Karroubi is a man who has helped more than anyone else with human rights cases and helped save people who were on the death row,” he said.