In February 2007, Koch resigned and challenged Sheets' successor,
William J. Phelan. Koch defeated Phelan 54% to 46% in that year's election. Koch defeated Phelan by a similar margin in a rematch two years later. Koch defeated Phelan once again in 2015, winning the first four-year mayoral term in Quincy's history. Koch also defeated then school committeewoman Anne Mahoney in 2011. A Democrat at the time, Koch endorsed Republican
Charlie Baker in the
2014 Massachusetts gubernatorial election. Baker's opponent, Democrat
Martha Coakley, alleged Koch endorsed Baker because Coakley unsuccessfully prosecuted Koch ally
Tim Cahill two years prior. Koch left the Democratic Party in 2018 because of his
anti-abortion views. Later that year, he endorsed Baker's bid for re-election in the
2018 Massachusetts gubernatorial election. Koch has served as chairman of the MBTA Advisory Board since 2011. In August 2021, the MBTA Advisory Board selected Koch to serve as its representative on the
MBTA Board of Directors. Following public outcry, in October Koch said the raise would be deferred until after the 2027 mayoral election. Later that month, Koch said the raise had been deferred in part due to an investigation by the State Ethics Commission. A campaign to put Koch's raise on the November 2025 ballot fell short of the required signatures. In May 2025, a group of Quincy residents sued to prevent Koch from installing statues of
Saint Michael the Archangel and
Saint Florian on Quincy's public safety building, alleging that the statutes would "unduly entangle the government with religion" and violate the Massachusetts Constitution by elevating one religion above others. The lawsuit is backed by the
ACLU, the
Freedom from Religion Foundation, and
Americans United for Separation of Church and State. Koch has justified the statues by saying that they “transcend religion and have a deep, long-held symbolic meaning of protection for our first responders. This is about them.” In October 2025, a Massachusetts Superior Court Judge issued an injunction prohibiting the city from installing the statues until the lawsuit is resolved. In January 2026, the Massachusetts Supreme Judicial Court agreed to hear the city's appeal of the injunction. On September 22, 2025, Koch drew condemnation for his statements on clergy sexual abuse, in which he alleged that that the sexual abuse of "13 and 14 year olds" by adult clergy members constitutes "mostly homosexual issues, not pedophilia." Koch continued that he never saw any sexual abuse in the Catholic church growing up and accused teachers, coaches, and the Boy Scouts of being the "real" perpetrators. On September 26, 2025, a group of sexual abuse survivors and advocates protested at Quincy City Hall. ==Personal life==