Question: Who were the leaders of the opposition of the party that dominated until the mid-20th century?

Knowledge 1: Philadelphia
From the American Civil War until the mid-20th century, Philadelphia was a bastion of the Republican Party, which arose from the staunch pro-Northern views of Philadelphia residents during and after the war (Philadelphia was chosen as the host city for the first Republican National Convention in 1856). After the Great Depression, Democratic registrations increased, but the city was not carried by Democrat Franklin D. Roosevelt in his landslide victory of 1932 (in which Pennsylvania was one of the few states won by Republican Herbert Hoover). Four years later, however, voter turnout surged and the city finally flipped to the Democrats. Roosevelt carried Philadelphia with over 60% of the vote in 1936. The city has remained loyally Democratic in every presidential election since. It is now one of the most Democratic in the country; in 2008, Democrat Barack Obama drew 83% of the city's vote. Obama's win was even greater in 2012, capturing 85% of the vote. [SEP] Knowledge 2: Republican Party (United States)
Founded in the Northern states in 1854 by anti-slavery activists, modernizers, ex Whigs and ex Free Soilers, the Republican Party quickly became the principal opposition to the dominant Democratic Party and the briefly popular Know Nothing Party. The main cause was opposition to the Kansas -- Nebraska Act, which repealed the Missouri Compromise by which slavery was kept out of Kansas. The Northern Republicans saw the expansion of slavery as a great evil. The first public meeting of the general ``anti-Nebraska ''movement where the name`` Republican'' was suggested for a new anti-slavery party was held on March 20, 1854, in a schoolhouse in Ripon, Wisconsin. The name was partly chosen to pay homage to Thomas Jefferson's Republican Party.
Knowledge 1: Politics of Texas
From 1848 until Richard M. Nixon's victory in 1972, Texas voted for the Democratic candidate for president in every election except 1928, when it did not support Catholic Al Smith. The state had a white majority and Democrats re-established their dominance after the Civil War. In the mid-20th century 1952 and 1956 elections, the state voters joined the landslide for Dwight D. Eisenhower. (Texas did not vote in 1864 and 1868 due to the Civil War and Reconstruction). [SEP] Knowledge 2: Civil rights movement (1896–1954)
Among the most prominent was Norris Wright Cuney, the Republican Party chairman in late 19th century Texas. These gains led to substantial discomfort among many white voters, who generally supported the Democrats. During the 1888 Texas Republican Convention, Cuney coined the term lily - white movement to describe efforts by white conservatives to oust blacks from positions of party leadership and incite riots to divide the party. Increasingly organized efforts by this movement gradually eliminated black leaders from the party. The writer Michael Fauntroy contends that the effort was coordinated with Democrats as part of a larger movement toward disenfranchisement of blacks in the South at the end of the 19th and beginning of the 20th century by increasing restrictions in voter registration rules.
Knowledge 1: Philadelphia
From the American Civil War until the mid-20th century, Philadelphia was a bastion of the Republican Party, which arose from the staunch pro-Northern views of Philadelphia residents during and after the war (Philadelphia was chosen as the host city for the first Republican National Convention in 1856). After the Great Depression, Democratic registrations increased, but the city was not carried by Democrat Franklin D. Roosevelt in his landslide victory of 1932 (in which Pennsylvania was one of the few states won by Republican Herbert Hoover). Four years later, however, voter turnout surged and the city finally flipped to the Democrats. Roosevelt carried Philadelphia with over 60% of the vote in 1936. The city has remained loyally Democratic in every presidential election since. It is now one of the most Democratic in the country; in 2008, Democrat Barack Obama drew 83% of the city's vote. Obama's win was even greater in 2012, capturing 85% of the vote. [SEP] Knowledge 2: Jeffersonian democracy
Jeffersonian democracy, named after its advocate Thomas Jefferson, was one of two dominant political outlooks and movements in the United States from the 1790s to the 1820s. The term was commonly used to refer to the Democratic - Republican Party (formally named the ``Republican Party ''), which Jefferson founded in opposition to the Federalist Party of Alexander Hamilton. The Jeffersonians were deeply committed to American republicanism, which meant opposition to aristocracy of any form, opposition to corruption, and insistence on virtue, with a priority for the`` yeoman farmer'', ``planters '', and the`` plain folk''.

Answer: anti-slavery activists, modernizers, ex Whigs and ex Free Soilers