What were the changing relations between the Soviet Union and the U.S. between 1917 and the 1950s?
Agree mostly with the answer above, here are a few additions. Immediately after 1917, when Russia was in civil war, we sided with the non-communists. The fact the communists won set bad blood between us from the beginning. During the Depression, communism became more popular in the US with the poorest Americans, which led to increased fear among government and the wealthy that some sort of revolution from within was possible. An anti-communist backlash was brewing socially here.
During World War II we were technically allies with the Soviet Union, but tensions were high and disagreements common even during the war. Some historians argue we deliberately held off on invading France so the Soviet Union would bleed more strength fighting Hitler. Stalin believed this whether it was true or not and it infuriated him.
Right after World War II the Cold War began, a period of intense competition, distrust and dislike between our two countries. A nuclear arms race began, we sent armies to Europe to face each other for a possible World War III (NATO vs. Warsaw Pact) and the government in the US stepped up anti-communist investigations. Richard Nixon actually got his start in Congress as a "red hunter" looking for American communists.
Briefly speaking (since a full answer would take a book), the relationship between the USSR and the US started out bad, got better, and then got to be really bad again during the time that you are talking about.
When the Soviet Union first came into being in 1917, the US tried to some extent to help destroy it. The US did not recognize the USSR until 1933. Then came WWII and the relationship got much better. During those four years, the two countries were actually allies.
But then immediately after the war, things got worse fast. The Cold War started and the two countries became mortal enemies.