When the king of Spain suggested to him that he shut up, Chavez was exposed before the world as a blowhard. It was a loss of face that started the freefall of popularity.
That is when the tide turned, but it also didn't help later when he sent his troops to the Columbian border, threatening to attack, and Columbia didn't even bother to respond. His troops just sat there for a day, and then went home. Who will fear him after that, no matter what he buys from Russia?