Sadly it's nothing new that the US government and agencies are intervening in the internal affairs of other smaller sovereign countries, and bullying them until they give in – especially when it comes to what it consider its sphere of influence. In this sense El Salvador for the US is not much different from Ukraine to the Russians, and they're not going to let them get "out of line" – be it too left leaning governments or challanges to the USD world reserve currency, like adopting BTC.

I would suggest checking out The Jakarta Method for a bit of an insight into how the US methodically have operated. Even though it started in Indonesia in 1965, it created the foundation for a strategy spanning over the last 60 years (almost), and probably still dictates how Latin American "issues" are to be handled.