I don't think it is anything to do with democracy. The Chinese have lent large sums of money to the Venezuelan government, and they are secured on assets. This is a known ploy of the Chines, and when the government can't repay, the Chinese claim the assets. There is no way that the US wants China to own land to set up a military base in Venezuela.

Another problem is the quality of oil in Venezuela, It is very heavy, and most of it is processed in the US.

Trump may have slipped up by supporting the interim president.