Get a load of this:

Now, [Obama] said, “we are called upon again.” To do what? Presumably to stand as one all over again, in the face of “new promise and new peril.” Included in the latter are terrorism, global warming, and nuclear proliferation. But those perils aren’t the worst of it. “The greatest danger of all is to allow new walls to divide us from one another.”
The sentence is the heart of the speech and an instance of Obama’s big weakness–his preference for the rhetorical flourish over a realistic account of things as they are. Most politicians share the weakness, and the preference has proved wildly attractive to Obama’s supporters. But think it through: “New walls to divide us” is just a metaphor, a trope. A trope can’t be the “greatest danger of all.” A terrorist setting off a nuclear bomb in London–that’s a danger. A revolution in Islamabad–that’s a danger. A figure of speech is just a figure of speech.

For goodness’s sake, read it all.