I believe that is why they perform contact tracing of known cases.
The major problems I see are still cultural. As far as I know, many people in the affected areas do not believe that Ebola is a real disease. Sick people do not go to the hospital because they believe that hospitals are killing people (for their organs, even). Getting people to understand the risks and take precautions is a challenge in that environment.
Americans are so used to the magic bullet they have no sense of hygiene like they did even in the '50s.
Complacency, instilled in a population by telling them "this is hard to get", coupled with normalcy bias, the hook-up culture of youth, the incredible potential for transmission via fomites, and sheer mobility will make this population low hanging fruit,indeed.
Aside from contact tracing being the equivalent of seeing what the bullet hit after it was fired (instead of stopping the shot), they have been trying to perform contact tracing there in Africa, and they seem to be having some trouble. People skip out there, they will here. How are you going to perform contact tracing in a major urban environment in the US?
Are you going to round up everyone who was on the subway or the bus with them?
Follow them around?
Where are you going to get the staff? Just a few confirmed cases could overwhelm that.
The saw about how much 'more advanced we are' won't carry the day.
A virus doesn't care about technology, about religious beliefs, about any of the social trimmings, it will infect the high or low of society with equal vigour given an opportunity.
Even closer to home, what is the lead time on manufacturing (importing?) sufficient PPE for even a few of the hospitals in the country--not just for the Ebola patients, but every patient who comes in the door--especially the ER--because you just don't know.
How about for EMS? (Was that car wreck because they were texting or because the fever was too high?--you see it all.)
Human nature is what it is.
Will the US close schools if cases start appearing? Likely that will be all too slow to happen, but could be a wonderful vector for the virus. People won't keep their sick kids home now.
I really wish I could be as sure this wasn't going to be a problem, and I seriously hope I prove wrong in this, but if this gets in the wild here in the US, it will be a plague of biblical proportions--not just because of the virus, but because of the fragile supply mechanisms that keep food on the shelves at the grocery stores, gas at the gas station, and the lights on, not to mention medical supplies distributed.
If that supply chain breaks, there will be a loss of civility or order imposed by force.
Neither is a pleasant prospect.
Consider that the very people who can prevent this in government are taking their marching orders from and serve at the behest of others who would jump at the chance to declare martial law and rule by fiat, and then consider the best way to defend against the disease is to not let it in, then why aren't we closing our borders to traffic from the affected countries at a minimum?