I first heard of a mysterious pneumonia cluster in Wuhan before Christmas and started recognizing it as something that could become a big deal in early January when we started seeing human to human transmission for sure. I because very concerned when I found out they were seeing asymptomatic transmission.
I remember a night in January when I couldn't sleep because it was very clear in my mind that too many people had fled Wuhan before they locked down. Given that there was asymptomatic transmission, and we had confirmed cases in the US already, it was likely spreading unseen already. Since we weren't testing anyone who didn't have travel history or contact with a known case we were not going to start catching community spread until somebody (or some cluster of people) became sick enough to prompt somebody to get testing done. I've been telling people for close to a month that they should assume it is already everywhere.
I have a basic understanding of epidemiology and an above average understanding of statistics. The President has people working for him who are world leading experts in both. There's no reason he shouldn't have known all of the things I just said were well within the margin to possible outcomes well before I did.
The known US cases as of right now is ~10,000. Given the geographic dispersion, lack of testing, and time the virus has been circulating unabated; I expect the actual number of cases is going to me orders of magnitude higher. I haven't tried to build a model or anything, and the confidence interval is going to be pretty big considering everything we don't know about the virus, but I wouldn't be surprised if somebody told me we had over a million cases in the US already. If we have less than 100K cases I would be absolutely shocked.