originally presidential candidates were selected by party caucuses in congress
Congressional nominating caucus The system was introduced after George Washington had announced his retirement upon the end of his second term, when the Democratic-Republican Party, and Federalist Party began contesting elections on a partisan basis. Both parties may have held informal caucuses in 1796 to try to decide on their candidates. After the disorganized electoral voting of 1796, both parties held formal caucuses in 1800 that selected their respective presidential candidates (prior to the ratification of the 12th Amendment in 1804 each party ran two presidential candidates). The Federalists secretly held their caucus in early May, but later made their ticket of President John Adams and Charles Cotesworth Pinckney public. The Democratic-Republicans also secretly met in May, and agreed to equally support Thomas Jefferson and Aaron Burr for president. The Federalists did not hold another caucus after 1800.[1]
United States presidential primary Delegates to the national convention were usually selected at state conventions whose own delegates were chosen by district conventions. Sometimes they were dominated by intrigue between political bosses who controlled delegates; the national convention was far from democratic or transparent. Progressive Era reformers looked to the primary election as a way to measure popular opinion of candidates, as opposed to the opinion of the bosses. Florida enacted the first presidential primary in 1901. The Wisconsin direct open primary of 1905 was the first to eliminate the caucus and mandate direct selection of national convention delegates. In 1910, Oregon became the first state to establish a presidential preference primary, which requires delegates to the National Convention to support the winner of the primary at the convention. By 1912, twelve states either selected delegates in primaries, used a preferential primary, or both. By 1920 there were 20 states with primaries, but some went back, and from 1936 to 1968, 12 states used them.