Your second sentence is inaccurate and isn't backed by history or the current US position in the world.
The US has certainly made military and foreign policy mistakes post WWII. Most historians and foreign policy experts would agree that Vietnam, US actions in Iran pre-1979, and probably now Afghanistan after 2004-5 were large failures. Iraq 2003 is also one IMO but that one is still being debated. I'll cover the last 30 years of Chinese relations in a sec. There are most definitely others I can't think of off the top of my head but those are the big ones.
Many times our failures and mistakes overshadow our successes. Korea, through the lenses of history, has been a large success. As was the outcome of the Cuban Missile Crisis, Just Cause, and Desert Storm. Our foreign and military policy also led to the fall of Soviet Union and winning the Cold War after 45 years of effort.
The United States is still currently the most dominant nation on the planet in terms of both hard and soft power (China has made large strides over the last 30 years to catch up but they're not there yet). Our network of allies and alliances have given the American public a security that few countries have enjoyed throughout history. The American people enjoy a standard of living matched by few other countries, based on our economic successes and our place in the liberal international order (I would agree that this is currently at risk due to short-sighted outsourcing of goods production, but that's for another post). The US Navy still dominants the seas and ensures the flow of goods both to and from our economy. No other country on the planet currently has the capability to conduct inter-theater military and humanitarian operations the way we can and do. The number of people across the globe wanting to emigrate to the US is testimony to how desirable the American way of life is.
None of those things listed above happened by accident; if everything the US has done post WWII was a "disaster", our place in the world and our ability to wield hard/soft power and influence/effect world affairs wouldn't be even close to what it is today.
If the invasion of Ukraine has proved anything to the Western world, it's that the last 30 years of thinking Russian, and more importantly China's exposure and integration into the world economic and information systems was going to lead to them embracing Western values and governance. The number of mass graves and destroyed cities in Ukraine should put the final nail in that coffin. That, IMO< has been a huge failure that we'll be dealing with for quite a while.