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.
Sovereign immunity will largely prevent creditors from collecting on any defaulted debt by the Venezuelan government, even debt secured by most assets.
Sovereign immunity is the fact that governments cannot be sued without their consent in their own courts, and some governments will extend this to foreign governments as well, depending on the specific circumstances.
It is effectively impossible to force Venezuela to give up any land located within the country without military intervention. The same is true for any assets (such as oil) located within Venezuela. The only assets that can potentially be seized are those outside of the country, so long as they are still owed by the government at the time of seizure.
This is a problem creditors of Argentina has had in the past. The Argentina government defaulted after granting US courts jurisdiction over disputes over specific debt, and creditors have had difficulty collecting via asset seizures after obtaining judgment because assets owned by the Argentina government are rarely located in jurisdictions that recognize the judgment.