Well it has entered the immigration debate, just as 9-11 did. So far, the ties made by guys like Grassley seem to me to be both vague and stupid.
Which is not to say that there isn't a more precise and more intelligent lesson for immigration policy in all this.
I think there is, but it's a lesson for a much narrower group of open border advocates. Some people who advocate openness oppose the visa process itself and think that no one should have to seek permission to come here. The government has no business keeping anyone out. This group quite literally wants open borders. No visas obviously also means no border security. Cases like this demonstrate why that might be a bad idea. Even if you support an open United States, it's probably still of value to check people out, identify a family or employer sponsor, and keep records.
I'll take a second to anticipate a red herring: of course this isn't going to prevent every incident. It obviously didn't prevent this incident, or 9-11 for that matter.
That misses the point. Good policy analysis thinks about these things on the margin and it considers the counterfactual. On the margin having some order to a policy of open immigration will improve security. The counterfactual case with no formal immigration process would make it far easier for terrorists, cartels, or anyone with bad intent to enter the country.
So that's not the sort of message that I suspect Grassley was trying to send, but it is a worthwhile point for literal open border types to consider.