We should keep them out of here.
That we can do pretty effectively ... if we have the will to do so. The problem is going to be working with governments like Canada who are lax on who they allow in.
Once termites start nibbling around the edges, the only way to stop them is to wipe them out. They don't have to be physically here to lob a nuke or other dirty device our way.
There are already enough "sleepers" ensconced on our ground to cause problems for some time to come - as we root them out, those in foreign lands will get itchy to find ways to attack - if we're totally reactive, we are saying that we are willing to sacrifice x-amount of American lives (Obama's policies) in order to not have to go where they breed.
It sucks, but reality is reality no matter how much we wish we could just mind our own business and let them do the same - they won't stick to themselves because it is their business to hurt us in any way they can.