This argument always comes up, and it's such a bad one when actually considered. The US was the largest world power, right? They also influenced all other western and/or capitalist nations, either through cooperation or threat of cutting them off from the market.
OK, so consider which communist/socialist countries failed. Did they fail in a vacuum? No. They failed with the "democratic" (often less democratic than the opposition, but this was their messaging) nations opposing them. For example, in Guatemala they elected a leftist president who introduced a minimum wage, increased democratic participation in elections, and the next president introduced land reforms to redistribute land to give it to the peasants.
Communism "always fails" because the most powerful nations in the world are afraid of it, so they do everything in their power to ensure it fails. The few that have been able to survive are dictatorships, because they can better withstand pressure from the outside. (This isn't to say dictatorships are good, just that they're more stable when attacked.) They also generally had or enforced cultural hegemony, for the same reason. It's survivorship bias.
We have no idea how well a leftist government would do if not attacked, because it's always attacked out of fear. If it's destined to fail, why are they afraid of it succeeding?