It won't take much to overwhelm the system. How many more carriers are already in the US and how long before one shows up in Mexico or Central America? What is Obama's plan to control it going to be then?
The current outbreak started just 6 months ago in Africa and the rate of growth isn't slowing. We might be able to contain it here but only if we can prevent new cases from being imported. That won't be possible with the current policies in place.
With 23 beds total at the five or so existing Level IV units in the USA, I'd guess #24 and up would cause the "overwhelmed" condition.
In Africa, healthcare workers were disproportionately infected because they received the patients at the time of their worst, most infectious condition -- immediately before, during, and after death.