As I say, watch the clips. The Federalist found at least 11 instances of Obama using the line about some Americans having come on the Mayflower and others on slave ships, which, you could argue, isn’t quite the same thing as saying “slaves are immigrants.” What’s striking about the clip of him below is that he does make that comparison, explicitly. And it’s that point that set the left on fire when Carson made it because it supposedly showed callousness to the fact that slaves were kidnapped and sent to America as property rather than migrating of their own free will. (Carson later posted something to Facebook noting that, yes indeed, he’s aware that slave migration to the . was involuntary.) It’s the same point in both clips in service to the same end, namely, that even people who came to America under the most oppressive circumstances shared the immigrant dream of a happier future for their descendants. But because Carson’s of the right and Obama’s of the left, that point is treated alternately as callous or hopeful as political circumstances require.