All politicians advocating for progressive social change, economic reform, challenging America’s racial caste system or advocating for women’s rights or LGBT rights, have been tarred as a socialist.
Political conservatism has been focused on blocking social change that challenges existing hierarchies since the French Revolution. Socialism emerged as the biggest threat to class hierarchies; conservatives have called everything they don’t like socialism ever since.
For example: "Segregationists claimed that the landmark Brown v. Board of Education decision, which banned school segregation, was the product of communist influence. “I have often wondered what was the source of the pro-Communist influence in the Supreme Court,” former Democratic Mississippi Sen. James Eastland declared as he demanded an investigation into communist influence on the court."