Ecuador is the Spanish word meaning Equator. Ecuador has the the Equator running right through it.
Panama is just north of Colombia, which is just north of Ecuador so it is the next closest country to the equator.
Puerto Rico is Part of the United States but assuming that Puerto Rico is being treated separately, and the actual "Lower 48" US States is what is meant by The US. Puerto Rico is next. Then the US.
However this is a trick question! The US has territories closer to the Equator than Puerto Rico, and even closer than the country of Panama. Baker Island at 0°11.7′N has the equator running through its territorial waters!
Panama is the closest South American Country to the USA.
Ecuador
Authentic panama hats are made in Ecuador. Due to economic problems in Ecuador and competition from Chinese hat producers production of panama hats in Ecuador is dwindling.
Ecuador and Panama
They use the US dollar as their currency in Ecuador.
Ecuador is a country, lying on the equator in South America. They use the American dollar as their official unit of currency and make "Panama" hats.
The Panama Canal passes through the country of Panama which is located in Latin America by Costa Rica, Puerto Rico, etc.
Ecuador borders southwest Colombia, and Panama borders northwest Colombia.
It's the official currency of Panama, and of course of Puerto Rico.
Ecuador is very close to Panama, as it is in South America.
If you consider Panama to be a North American country. (Since the canal runs through it, the country is divide between the north part of the country which is in North American and the southern part which is in South America.) If Panama is considered, the answer is Panama City, Panama. If not, the closest exclusively North American capital is San Jose, Costa Rica.
He liberated Bolivia, Venezuela, Colombia, Ecuador, Panama, and Peru.