Truman ran with Senator Alben W. Barkley of Kentucky, while Dewey's running mate was Governor Earl Warren of California.

Once a typical Yankee Republican bastion in the wake of the Civil War, Massachusetts had been a Democratic-leaning state since 1928, when a coalition of Irish Catholic and other ethnic immigrant voters primarily based in urban areas turned Massachusetts and neighboring Rhode Island into New England's only reliably Democratic states.

Notably, Truman flipped highly populated Middlesex County, in which did not vote for any of Franklin Roosevelt's four victories in the state, into the Democratic column.

[2] Massachusetts and neighboring Rhode Island were the only states in the Northeast to favor Truman over Dewey in 1948, the same split that had occurred in 1928.

Both states had large urban Irish Catholic populations, who remained loyal Democrats in the wake of 1928, even as other groups defected back to the GOP.