Long time lurker, first post. I live in the US and as much as I ish it were otherwise there won't be any pressure on this side of the Atlantic against Miller's bid. Irish America pressure groups have been in decline for decades and are riven by factionalism. When they do act it tends to be on issues like immigration reform (again a pressing issue) or easily graspable media issues like a negative portrayal in a film or TV show. If Miller was in a retail business that could be easily boycotted it might be a different story, but no tow company operator is going to let a far away soccer team influence a major business decision like buying a truck. As for general far right nastiness, anti-Catholic prejudice has declined so steeply in the US that most people have a very hard time taking it seriously when there are bigger home grown divisions. The ADL really won't care.
The real question for me is whether Miller has any idea of what a rotten pup he is buying. Having spent many years in soccer pubs explaining my support of Celtic and Scottish football to Americans who are overwhelmingly fixated on the EPL, Mexican teams and a handful of global giants like Barcelona I can attest to how difficult it is to explain the nuances of the old firm to people who come from a sporting culture where nothing similar has ever really existed. US sporting affiliations are overwhelmingly local or based on personal history (where you went to University). There aren't political affiliations tied to teams like in Italy and Germany, and while some teams have been more popular with minorities because of groundbreaking players that changes when the players change (e.g. Boston in the NBA was for a time viewed as a "white" team, but that ended quickly). I have a very hard time believing that Miller grasps the nature of the peepul and how toxic the brand is throughout the UK. I'm fairly sure if Miller read a stack of Rangers Media posts he wouldn't understand what separates that cesspool from, say, an particularly active forum involving QPR. You need some background to get the "tarrier" references and the crab flute thing.
On the plus side, if Miller thinks there is an untapped market for Rangers in the US he is delusional. The SPL only got on cable here this season and the EPL has been making converts at a very rapid clip. Watching the dregs that will be left after off-season departures isn't a compelling sporting case when you can in good conscience pick ManU or Barca to support, and unlike Celtic there isn't a large pool of people with a potential sentimental attachment to the idea of the club. Most Scots came to the US a very, very long time ago and to the extent thy think of their Scottish roots at all they think of glens, bagpipes and Braveheart not Govan, flute bands and Knox. In my experience the type of evangelical Christian who might buy ino certain aspects of Rangers....err...appeal loathe soccer almost as a point of pride. Celtics appeal in the US is limited compared to the EPL, but Rangers is nonexistent.
I think Miller is probably a smart businessman and is planning to run the club with ruthless fiscal discipline, sanctions or no sanctions. I just don't think he realizes the backlash that will follow.
Sorry for the long first post, but figured I'd add a perspective from this side of th Atlantic since the issue was raised.