Re: The jist of this U.S. government intervention will be...
To the best of my knowledge, the US government doesn't really have a say on how much is invested by US companies in Ireland. It could of course create laws against doing so, but that would probably break every treaty in the book.
It's nice that governments are finally getting involved. It's a bit silly that companies (which are not all the size of Facebook) have to bear the brunt of what is essentially a political dispute.