What were the causes of the conservatives moving from the democratic to the Republican Party?

The main reason conservative voters went from supporting the Democratic Party to supporting the Republican Party stems from the New Deal carried out by the President Roosevelt government in the 1930s. During that time, the Democratic government began to carry out a series of social and labor policies that greatly expanded public spending, promoted the redistribution of income, created new rights, and expanded the role of government in society. These policies, directly influenced by Keynesianism, were contrary to the traditionally conservative positions of the Democratic Party; it could even be said that they were the policies raised up to that moment by the Republican Party. Consequently, all of American politics shifted towards liberalism until the irruption in the 1960s of Barry Goldwater as a conservative opponent within the Republican Party, which caused the majority of conservative voters to begin supporting that party from that time on.

necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.