If I were Mitt, I would have attacked Obama's use of an executive order to pull this stunt. He could have done that without actually giving a comment on pro-/anti- illegal immigration, and still managed to have made some respectable comments regarding the abuse of executive orders. Of course, Romney blew that opportunity because he doesn't respect the constitutional process for making laws, either.
Obama is quickly becoming one of the worst presidents to legislate via executive orders because he thinks that 'Congress moves too slow' (it's supposed to, Mr. President, and I'd be happy if it stopped moving). I'd put him up there with FDR in terms of broad-reaching executive orders.