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.
They do like to maintain their influences. US foreign policy doesn't have a good reputation. Too many lies, deceptions, and breaking promises. I will take a look at the Jakarta Method when I get a chance. Most frustrating part is, these senators don't have anything better to offer.
Yes, the incompetance of US officials is also a good observation when it comes to where the US Empire is in its life cycle. Corruption breed incompetence (which breed more corruption) when it comes to officials, and is symptomatic of a degenerating state.
Even if the US government didn't use any less diablolical methods during the 60s and 70s, they still did pride themselves in having the most competent people in important positions. It seems to me like this has degenerated over time, and increasingly become more about how much you're able to pay for a position. You certainly don't need to think Kissinger is a nice person, but it's hard to argue that he was an incompetent diplomat.