As the U.S. Constitution did not contemplate, let alone regulate, political parties, there was no established method for deciding on the nominees of political parties for national office. At first, nominations were determined by caucuses of each party's members of Congress. The caucus system came under fire with the rise of the Jacksonian Democrats in the 1820's. Widely regarded as undemocratic, the system was subjected to increasing pressure to abolish it and replace it with something better. Typical of the criticisms were those expressed by Felix Grundy in the Tennessee legislature in 1823:
It has been said that the members of Congress in caucus only recommend to the people for whom to vote, and that such recommendation is not obligatory. This is true and clearly proves that it is a matter which does not belong to them - that, in recommending candidates, they go beyond the authority committed to them as members of Congress and thus transcend the trust delegated to them by their constituents. If their acts had any obligatory force, then the authority must be derived from some part of the Constitution of the United States and might be rightfully exercised; but when they say they only recommend, it is an admission, on their part, that they are acting without authority and are attempting, by a usurped influence, to effect an object not confided to them and not within their powers, even by implication.The caucus system died quickly. The first national convention held to nominate candidates for president and vice-president was held by the Anti-Masonic Party in 1831, followed by the National Republicans later that year. The Democrats followed suit in 1832 and the practice became standard thereafter. National conventions are designed to present the appearance of unity, but sometimes they fail badly. In the Election of 1860, the Democrats first convened in Charleston, South Carolina, but Southern Democrats wouldn't agree with the North, so they reconvened in Baltimore to pick their own. After the war, opponents of Grant in 1872 formed the "Liberal Republican" party In the Election of 1912, the Republican convention renominated William Howard Taft, which angered the progressives who split off and formed the Progressive Party, better known as the Bull Moose Party after its candidate, Theodore Roosevelt. The push by Hubert Humphrey to include a strong Civil Rights plank in the Democratic Party platform in the election of 1948 resulted in a walkout by segregationist Southern Democrats, who held a convention in Birmingham, Alabama, and nominated Senator Strom Thurmond of South Carolina. At other times, political splits have taken place even before the national convention. The "liberal Republicans" who opposed Grant in 1872 held their national convention in May, while the regular Republican didn't meet until June. Beginning with the first Democratic National Convention in 1836, the "two-thirds rule" required that the successful nominee gain the support of two third of the delegates. This gave a disproportionate influence to Southern states, who could effectively block unacceptable candidates. The rule was abolished in 1936. The Republican conventions only required a majority for nomination.