Originally, the GOP subscribed to what is referred to as classical liberalism with ideological stands that were anti-slavery and pro-economic reform. The party was usually dominant over the Democrats during the Third Party System and Fourth Party System. In 1912, Theodore Roosevelt formed the Progressive ("Bull Moose") Party after being rejected by the GOP and ran as a candidate. He called for many social reforms, some of which were later championed by New Deal Democrats in the 1930s. He lost the election and when most of his supporters returned to the GOP—they were at odds with the new conservative economic stance, leading to them leaving for the Democratic Party and an ideological shift to the right in the Republican Party. The liberal New Deal Democrats dominated the Fifth Party System at the national level. The liberal Republican element was overwhelmed by a conservative surge begun by Barry Goldwater in 1964 and fulfilled during the Reagan Era.
Currently, their ideology is American conservatism, which contrasts with the Democrats' liberal platform and progressive wing. The GOP's political platform supports lower taxes, free market capitalism, free enterprise, a strong national defense, gun rights, deregulation and restrictions on labor unions. In addition to advocating for conservative economic policies, the Republican Party is socially conservative and seeks to uphold traditional values based largely on Judeo-Christian ethics. The GOP was strongly committed to protectionism and tariffs from its founding until the 1930s when it was based in the industrial Northeast and Midwest. Since 1952, there has been a reversal against protectionism and for free trade. After the Civil Rights Act of 1964 and the Voting Rights Act of 1965, the party's core base shifted, with the Southern states becoming more reliably Republican in presidential politics and the Northeastern states becoming more reliably Democratic. The party's core support since the 1990s comes chiefly from the South, the Great Plains, the Mountain States and rural areas in the North as well as from Orthodox Jews, Catholics, Mormons and Evangelicals nationwide.
Along with the GOP winning 24 of the last 40 presidential elections, there have been a total of 19 Republican Presidents, the most from any one party. The first was 16th President Abraham Lincoln, who served from 1861 until his assassination in 1865; the most recent being the 45th and current president Donald Trump, who took the oath of office on January 20, 2017.
As of 2018, the Republican Party is the primary party in power in the United States, holding the presidency (Donald Trump), majorities in both the House of Representatives and the Senate, a majority of governorships and state legislatures (full control of 32/50, split control of five others). Furthermore, the GOP presently hold "trifectas" (the executive branch and both chambers of the legislative branch) in a majority of states (26/50) and a "trifecta plus" (executive, legislative and judicial branches) at the federal level (as Republican Presidents appointed five of the nine Supreme Court justices).
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.