In the time since WWII, American public opinion about international involvement has not been monolithic and it has not been constant. Different people have had different opinions and opinions have changed over time.
Most people during the Cold War era were in favor of US involvement overseas. They felt that the US needed to be aggressively involved in foreign affairs so as to contain communism. There were some who believed in a more isolationist attitude, but they were in the minority.
After the end of the Cold War, things became much more muddled. Nowadays, there are many different opinions on international involvement. Some people believe the US should be isolationist rather than wasting our money and the lives of our soldiers in places that do not directly affect our national security. Others argue that we should aggressively act in the international arena to protect our interests. They say that we should use our power to do things that allow us to keep our status as the world’s only superpower. Still others argue that we should be involved in other countries so as to improve them. We should try to use our power to spread democracy.
All of these views exist today, making public opinion today much less clear than it was in the Cold War.