John Spencer served in the United States Army during the Vietnam War, earning a Combat Infantryman Badge and a Bronze Star. After his military service, he pursued a career in construction and real estate, eventually becoming a vice president at Bankers Trust Co. Spencer entered public service as a member of the Yonkers City Council, where he served for four years as the Republican majority leader. He then became the Mayor of Yonkers, during which he focused on economic development, tax cuts, and ending state and federal control over city affairs. Spencer founded Spencer Consulting Group, which specializes in addressing alcoholism.

John Spencer's political identity is marked by a blend of fiscal conservatism and socially conservative values, tempered by a pragmatic approach to governance. His tenure as Mayor of Yonkers showcased a knack for economic revitalization through strategic tax cuts and development projects, while his Senate campaign highlighted staunch opposition to abortion and gun control. Spencer's unexpected support for tighter border security and endorsement of the Iraq War reveals a willingness to align with controversial federal policies, suggesting a complex ideological landscape. His political career, marked by initial advocacy for term limits followed by efforts to rescind them, underscores a certain ideological flexibility.