The First Presidential Primary

New Hampshire holds the first presidential primary election in the nation every four years, a tradition that has given the small state outsized influence in American politics since 1920. The primary is so important that presidential candidates often spend months in New Hampshire greeting voters at diners, town halls, and living rooms, creating a retail politics culture where ordinary residents can realistically expect to shake a candidate's hand and ask a direct question. Several candidates who have won the New Hampshire primary have gone on to lose the nomination, but no one has ever won the presidency without first competing seriously in New Hampshire.

Source: Wikipedia