<P> Starting with the 1796 election, Congressional party or a state legislature party caucus selected the party's presidential candidates . Before 1820, Democratic - Republican members of Congress would nominate a single candidate from their party . That system collapsed in 1824, and since 1832 the preferred mechanism for nomination has been a national convention . </P> <P> The first national convention was called by the Anti-Masonic Party in 1831, as they could not use the caucus system because they had no Congressmen . The party leaders instead called for a national meeting of supporters to select the party's candidate . This convention was held in Baltimore, Maryland on September 26, 1831 which selected William Wirt as their Presidential candidate . </P> <P> 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 . </P> <P> The primary received its first major test in the 1912 election pitting incumbent President William Howard Taft against challengers Theodore Roosevelt and Robert La Follette . Roosevelt proved the most popular candidate, but as most primaries were non-binding "preference" shows and held in only fourteen of the - then forty - eight states, the Republican nomination went to Taft, who controlled the convention . </P>

When were voters first invited to participate in the presidential nomination process