Final answer:
The election of a conservative Republican Congress in 1946 was caused by a combination of factors, including dissatisfaction with President Truman, effective Republican campaign messaging, and a larger conservative shift in US politics.
Step-by-step explanation:
The election of a conservative Republican Congress in 1946 was caused by a combination of factors. One of the main factors was the dissatisfaction of voters with President Truman and the Democratic Party, who were seen as straying too far from the principles of the New Deal and being too similar to previous President Franklin Roosevelt. Republicans also used slogans to attack Truman during the election, and their message resonated with voters who believed that the new president was not effectively addressing their concerns. Additionally, the increasing conservative shift in US politics, which had been ongoing since the 1920s, played a role in the election outcome.