It's the oil, stupid. But there's way more than meets the (oily) eye.
Caracas has committed the ultimate cardinal sin in the eyes of Exceptionalistan; oil trading bypassing the US dollar or US-controlled exchanges.
Remember Iraq. Remember Libya. Yet Iran is also doing it. Turkey is doing it. Russia is – partially – on the way. And China will eventually trade all its energy in petroyuan.
With Venezuela adopting the petro crypto-currency and the sovereign bolivar, already last year the Trump administration had sanctioned Caracas off the international financial system.
No wonder Caracas is supported by China, Russia and Iran. They are the real hardcore troika – not psycho-killer John Bolton's cartoonish "troika of tyranny" – fighting against the Trump administration's energy dominance strategy, which consists essentially in aiming at the total lock down of oil trading in petrodollars, forever.