This is the heart of Mr. Chertoff's statement and it in no way implies a position of isolationism:

Mr. Chertoff said, "We can do a good job with the known terrorists, if we have their name, or if we've previously arrested them and have their
fingerprint on file" but a more potent threat was the terrorist with no known form. The fear has always been the so-called ‘clean-skin' —
that's a person whose documents are completely legitimate — are not forged."
This had led America to require a significant tightening of the rules for passengers traveling under a visa waiver. Among the new requirements is that
all passenger information be transmitted to the U.S. before a plane takes off. Soon, passengers will have to give all 10 fingerprints, rather than
just two.
"If someone's a terrorist, and they've left their fingerprints at a training camp, or in a safe house where a bomb was built, and those latent
fingerprints are collected, we can then, when someone crosses a border, match their real prints against those latent prints... even if we don't know
their name," he said.
www.nysun.com...
The US has every reason to suspect that another terrorist attack is inevitable and that if it were not for a heighten level of awareness, another one
would have already happened.
America does not desire isolationism. Indeed, this is what Mr. Chertoff had to say about immigration:

"Our Muslim population is better educated and economically better off than the average American. So, from a standpoint of mobility in society,
it's a successful immigrant population.
To some degree, the whole country is a country of immigrants, and therefore, there's no sense that we
have insiders or outsiders. [emphasis mine]
www.nysun.com...
Given the level of the threat, it is imperative that we know who is coming into our country and that is all Mr. Chertoff is saying.
Personally, I don't think we're doing enough in that regard, but that's beside the point.
[edit on 2007/4/5 by GradyPhilpott]