The problem really is with the drivers. You're looking for the best of the best, and the driver pool with F1 potential isn't that big from the start. I don't think trying to acquire American mechanics for USF1 is a problem at all, nor would be trying to keep their car American-made, etc. I'm not saying that they won't be able to find some very good American drivers which could end up highly successful, I just think it's a very bad idea to keep it to American drivers in an area where there's not that many people to choose from anyway.
Who knows, they might end up testing like 20 American drivers and find none that fit for the job. Then what would they do? Hire the best of them, even though he's not good enough, and hope that the mechanics make up for it? That would be ridiculous.
Nationalism is really not a good idea in F1. It's mostly not a good idea in team sports as a whole. For instance, have a look at Olympic teams (or world championship teams, etc). They're never as good as the teams found in the pro leagues, because they have to keep it to players of only one nationality. And yes F1 is a team sport.
p.s. Thanks for the topic name change, I failed at capital letters