The 1948 Presidential election in Boston, in the Contest between President Harry Truman and New York Governor Thomas Dewey, here Truman's spectacular performance with Irish Catholics led to him besting the Governor, garnering Truman an astounding 41.4% margin over Dewey, aiding the president in winning Massachusetts that year.
Something that has been attributed to providing Truman's strength on this win was the simultanious holding of the controvercial Contraceptive or Planned Parenthood referendum which galvanized and turned out the city's Catholics who—as a key Democratic constituency—voted for Truman and against the referendum.
Being defeated by 14.7% Statewide and by 33.4% in the City of Boston, the referendum would have allowed for Physicians to give treatment or perscriptions to married woman to prevent pregnancy if a pregnancy would have threatened the life of the mother.
Here, the referendum helped Truman aproach the Democratic high water mark of the presidential election of 1936, and due to the Galvanizing effect of the referendum, Truman ended up winning more votes in Boston than Roosevelt did in his four runs for the White House.