Tariffs might keep Chinese EVs out of the US, but they don't stop US influence from fading everywhere else. South America is voting with their wallets, and 'buy American' doesn't work when the price is double and the tech is the same.
Unless the US intends to sanction every country that prioritizes value over US geopolitics, this battle is already lost.
In South America there's also no anxiety over China becoming a superpower, which may be an argument against Chinese products in the US.
In fact, China has pretty good relations with most South American countries. Likely better than the US. I wouldn't be surprised if many people view China more favorably.