I'm kind of torn over which part of this is more offensive; suggesting Obama doesn't understand the UK because he lacks an Anglo Saxon heritage, or the idea that we might be dumb enough to swallow it.
Just kidding. It's the first one.
I suppose I could point out there's plenty of white Americans would be pretty annoyed if you called them Anglo Saxons - like say the Italian-, Norwegian-, Polish- and German-Americans, pluse of course the Irish-Americans, who'd tear Romney's guts out if he chucked that term their way - and pissing them off to court David Cameron is a pretty stupid choice.
I could also point out that, the Daily Telegraph's typically milquetoast statements on anything to do with race notwithstanding - this "may prompt accusations of racial insensitivity" in roughly the same way that consuming a cement mixer may prompt suggestions of a lack of dietary balance - that's a spectacularly offensive statement from a British perspective as well. My girlfriend isn't Anglo-Saxon. Plenty of my buddies aren't Anglo-Saxon, or of any European heritage in general. I grew up in a part of the country where there's a non-trivial chance of being closer to a Viking than anyone from a German tribe, and an hours drive from places where you're more likely to have the Ganges run through your ancestral veins than you do the Rhine.
Instead, though, let's focus on the main point: Mitt Romney wants the UK to believe that we share less in common with a Protestant whose father came from the Commonwealth than we do with a man from a country that fought a war against us when we wouldn't let them slaughter enough Native Americans for their liking, and who belongs to a religion that believes magical underpants are given to them by American Jesus, which is why they get to posthumously baptise Jewish Holocaust victims.
There are weirder things than being black, is my point.