[Goose]

I guess my point was simply that unless every county health commissioner is doing this, if others aren't, and those contagious patients go across county and state lines, it starts all over again. In this sense, the spillovers are unavoidable and the only way to fix it is a consistent, nationwide response.

You are correct that a trace and test strategy can be overwhelmed by an influx of infected people from elsewhere. It is necessary that each county at least keep the cases down to a dull roar. If we are all at about the same point when the controls start being lifted, that should be possible. As for a consistent nationwide response, I don't think so. As Dr. Fauci has pointed out, each situation is different. The entire population of Lincoln County Nevada could be positive and move to Santa Clara County tomorrow. That would be problematic but not overwhelming. Lincoln County doesn't need and can't do what Santa Clara and San Mateo can and must do.
Late Addition: Dr Birx talked about exactly this issue today at the daily briefing. What she said wasn't as detailed as I would have liked, but she did have a  lot to say about contact tracing in counties with low infection levels.

Taiwan wouldn't have simply 1/2 the success it's having if 1/2 the island declined to test, contact trace, and isolate, because it only takes a few rotten/contagious apples to re-spoil the whole barrel.

Actually, no. It takes a critical mass of contagious apples to spoil the whole barrel. China is dealing with that situation now. So is Singapore. So far, so good. However, they could end up being overwhelmed if there are too many, just as Santa Clara county could be. It isn't going to be easy to do since we are starting from such a weak initial capability. If we fail at this, we have the possibility of a big rebound, and generating the political will to go back to shelter-in-place will be difficult to impossible. Many will justly ask "It didn't work the first time. Why take the economic hit again if it won't work?".

[Goose]

I guess my point was simply that unless every county health commissioner is doing this, if others aren't, and those contagious patients go across county and state lines, it starts all over again. In this sense, the spillovers are unavoidable and the only way to fix it is a consistent, nationwide response.

You are correct that a trace and test strategy can be overwhelmed by an influx of infected people from elsewhere. It is necessary that each county at least keep the cases down to a dull roar. If we are all at about the same point when the controls start being lifted, that should be possible. As for a consistent nationwide response, I don't think so. As Dr. Fauci has pointed out, each situation is different. The entire population of Lincoln County Nevada could be positive and move to Santa Clara County tomorrow. That would be problematic but not overwhelming. Lincoln County doesn't need and can't do what Santa Clara and San Mateo can and must do.
Late Addition: Dr Birx talked about exactly this issue today at the daily briefing. What she said wasn't as detailed as I would have liked, but she did have a  lot to say about contact tracing in counties with low infection levels.

Taiwan wouldn't have simply 1/2 the success it's having if 1/2 the island declined to test, contact trace, and isolate, because it only takes a few rotten/contagious apples to re-spoil the whole barrel.

Actually, no. It takes a critical mass of contagious apples to spoil the whole barrel. China is dealing with that situation now. So is Singapore. So far, so good. However, they could end up being overwhelmed if there are too many, just as Santa Clara county could be. It isn't going to be easy to do since we are starting from such a weak initial capability. If we fail at this, we have the possibility of a big rebound, and generating the political will to go back to shelter-in-place will be difficult to impossible. Many will justly ask "It didn't work the first time. Why take the economic hit again if it won't work?".