[SmokingJoe]

It's not mutually exclusive. You don't have to be disloyal to America to be loyal to Britain. The two countries have been allies for decades. Britain is America's closest ally.
However, if any of them should be foolish enough to want to run for president(just kidding), they are gonna have to renounce their US citizenship, and even after that they'd be raked over the coals by birtherism. I wouldn't recommend it myself.

[SmokingJoe]

Correction. Should Read:

However, if any of them should be foolish enough to want to run for president(just kidding), they are gonna have to renounce their UK citizenship