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Adar first runs for mayor of Caprica City, to which he is elected, and later goes on to successfully run for president (TRS: Miniseries; "Daybreak, Part II"). At the time of the Cylon attack, he has nine months left in his second term (TRS: "Bastille Day").
Adar appears to be a somewhat controversial president; William Adama considers him to be a "moron" (TRS: "Home, Part II"). At some point in his presidency, he deploys Colonial Marines on Aerilon, an action which results in casualties and a public outcry. Though publicly he stands by his decision, he personally regrets his actions and writes down the names of all the casualties, leaving it in his desk as a reminder of his fallibility. His successor emulates the same practice after the loss of Olympic Carrier (TRS: "Water").
Nevertheless, Adar continues to possess rather aggressive tendencies as president, as he is willing to use military action to resolve a drawn-out teacher strike when the teachers start to become violent. When his Secretary of Education, Laura Roslin, negotiates a diplomatic solution with the teachers' union, he is less than pleased at this outcome and asks for her resignation, which she refuses to discuss until her return from the decommissioning ceremony aboard Galactica (TRS: "Epiphanies").
While in office, Adar offers a full pardon to Tom Zarek in exchange for the latter's renunciation of violence, which Zarek turns down (TRS: "Bastille Day"). Despite being a married man, Adar engages in an illicit romantic affair with Laura Roslin during the last days of his administration (TRS: "Epiphanies"). He is also an influential friend to Dr. Gaius Baltar (TRS: "Miniseries"). All three persons go on to succeed him as president.
Following the nuclear attack on Picon by the Cylons, Adar offers a complete, unconditional surrender on behalf of the Twelve Colonies. The Cylons ignore the overture, and Adar likely dies soon after, possibly following the detonation of a nuclear weapon over Caprica City. As a result of his death, the automated Case Orange government continuity mechanism activates via wireless and attempts to locate any surviving government officials. Only Roslin, the forty-third official in line of succession, responds, and she succeeds Adar as president after being sworn in aboard her government transport, a passenger liner designated Colonial Heavy 798 (TRS: "Miniseries").