So put a fence around Dallas for 3 weeks. Of course it would have been simpler and cheaper to quarantine all passengers from certain areas first. But this is your guberment at its finest.
Contact Tracing will allow you to do that in a more “targeted” manner. For example, you quarantine the family. You look for symptoms among them. If they have any symptoms or develop symptoms you take the trace back one layer or two.
The circle can go wider, but it need not impact the entire city area of Dallas.
Public health officials have the authority to step in and force this. And they will.
What is going to happen is that someone who has a public job is going to be infected and they will refuse to go get treatment because they know what that will mean. They will continue to go to work because they need to make money or because their boss is an idiot who whines about them calling in sick.
THIS is what would cause wide spread infection.
It would be cheaper to not allow flights from those countries but that defeats the politicians point which is to spread it....if it it was not the point of this whole exercise then those countries would have already been quarantined by the powers that be.