Are you saying that a massive change in circumstances such as 9/11 does not merit a change in position toward a significant increase in border and immigration control? Such a change in position would be a "flip-flop"? I strongly disagree.
No one has any intention of sealing the borders, so no, I don't think 9-11 makes a diffence. If bad guys want to get into the US, we probably can't stop them. Does anyone really expect the entire border around the whole of the US to be sealed tight and locked? Dream on.