In my opinion, support for border control is slowing building. Give it ten years.
As for SARS, once it hits Mexico, this will strengthen support for border control, but will still not be enough to make it a reality. I'm basing that on an expectation that Mexico will manage to institute effective quarantine and infection control when needed. Plus, even if they only do a middling job, the liberals will say that legal entrants from Mexico to the US might also have SARS. Which will be a complete crock, since legal entrants get better medical care while in Mexico.