Why did reagan switched party affiliations in the 1950's?

Two very particular issues drove Reagan's political conversion: fiscal policy and anti-communism. In the late 1940s, Reagan was facing the end of his career as a movie actor and was finding less and less work. He was upset because he felt that he had only a short window to maximize his earnings and ensure his future financial security and that the present 90% top marginal rate was unreasonable. 
Reagan's experience as a board member and later president of the Screen Actors Guild also moved him politically rightward. In this professional capacity he dealt with a strike by a set builder union backed by communist sympathizers.