In early 1968, Galbraith endorsed Senator Eugene McCarthy, who ran against Johnson on an anti-war platform. During the New Hampshire Democratic primary, Galbraith toured the Granite State, giving pro-McCarthy speeches in churches, union halls, campuses and house parties. As McCarthy had the reputation of being strange and frivolous, Galbraith's support and campaigning for him was important, as McCarthy needed the endorsement of mainstream figures to give him credibility. When the New Hampshire Democratic primary was held on March 12, 1968, Johnson defeated McCarthy by only about 300 votes, a humiliation for an incumbent president with a well funded campaign running against a senator widely considered to be too eccentric to be president, and who had only a fraction of the campaign money that Johnson had. Through Johnson won the primary, the very narrow margin of his victory was widely considered to be a defeat. On the night of the primary, Galbraith celebrated the result at McCarthy campaign headquarters as if it were an outright victory. The day after the New Hampshire primary, Galbraith was widely cheered by his students when he entered his lecture hall at Harvard.
