"I see America as an interfering country. They seem to think they can demand and do whatever they like to other countries, as though they are in charge.

You did not link to the original article you mention, so 'exactly' who was involved from the US senate is not clear.

"As a British citizen, I am somewhat suspicious that the US senate think they are a higher court of authority than any equivalent in other countries"

Again.... just as we have STATES which are more conservative, we also have SENATORS who are conservative and take it on themselves to go on 'missions', often under the auspices of some religious group. They do NOT speak for or represent either the Senate OR the US as a whole.
*IF* some US senators appeared to meddle or criticize the workings of the Scottish government, they should be ashamed....but so far I have no idea what prompted the cardinal to say what he did.

I think *I* will see if I can sort out what actually occurred using Google.