This virus evolves somewhat slowly- up to 2 weeks incubation period plus another 3-6 weeks of illness. But because it spreads during incubation, and has a high R0 value, once it starts spreading it does extremely rapidly in dense areas, after the 1-3 week lull. It is allegedly aerosolized and one paper reported surface contamination for >1 week.
The us is in week ≈2 now. Week ≈3 is where the whole country lights up with outbreak and the government is pressed into extreme measures. This is based primarily on South Korea's timeline.
On the bright side, the sprawl of the US may make this easier to deal with, but you can probably expect some domestic travel restrictions soon. I don't know if states have authority to close borders but I won't be surprised to hear about it.