If the US or State governments are doing widespread tests, quarantining the sick, and/or tracing contacts, that effort is a deep dark secret - or (my suspicion) the effort is being squandered by "trying to be strong everywhere at once" and dividing the supplies into penny packets that go to every large city, where they are swallowed up like a drop in a bucket. We are not getting anywhere - new cases keep arising - even though the entire population was put under quarantine long enough ago to catch asymptomatic carriers and remove them from crowds.
The US federal government is using a single built-in excel function to predict what the spread of Covid-19 is doing. The US federal government isn't "trying to be strong everywhere", it is simply being incompetent.
Various state governments pandemic responses where predicated on a CDC that wasn't being incompetent (as was Canada's; Canada's central health agency was planning to coordinate with the CDC. But the CDC is hamstrung and not doing it.). They are scrambling to deal with this pandemic with zero to negative federal assistance.
Very few parts of the world have the testing capacity to mass test the population. Very few parts of the world have a public health infrastructure needed to contact trace positive cases and notify the people who are at risk to get a test. And this is reasonable; you need a
LOT of work per positive result to do effective contact tracing in any kind of traditional way.
To do it non-traditionally, you need a central pandemic response that isn't incompetent and has the expertise for this sort of thing. Not many US states have a full-fledged set of pandemic experts on staff; and, the US federal response is hamstrung by its executive leadership, who is pushing for quack cures and reopening, instead of going to war with it.
Instead, what we have is untraced community spread. Social isolation can bend R0 -- reproductive number -- down, but it takes a serious and uniform effort to get it under 0. The US response, patchwork, means that R0 is at or above 1 in most of the country (geographically, and possibly population wise). Only in areas where the local government saw a disaster coming does it go below 1 (washington state, some areas of california, new york). And often too late. NYC is going to hit about 30% infection even with a shutdown.
To extinguish this quickly, you have to shut down
before the 2nd death ideally, and definitely before the 12th. Washington got "lucky" in that it killed a bunch of people in an old folks home "early", so they had the political capital to do a shutdown earlier than most areas do.
NYC got unlucky, as apparently the subways meant that their R0 was insanely high, and by the time they responded it was everywhere.
Remember, if it doubles every 4 days and 1% die about 20 days after getting it, by the time the first person died you had 2^5*100 = 3,200 people infected. And 50 days later with uncontrolled spread 1 million are infected.
NYC had it doubling every 2-3 days instead of every 4 during that period, and did lockdown when around a dozen died. 20/2 is 10, 20/3 is 7, so 2^(7 to 10) * 100 * 12 150k to 1.2 million infected.
It is the places where there are no cases and nobody dead that need to lockdown to prevent this from growing. Then you need to reduce mobility and start contact tracing every new diagnosted case, and testing everyone with any symptoms whatsoever with a rapid turn-around test.
All of this requires central proactive leadership aimed at wiping out Covid-19, that the USA is lacking. The US central leadership is complaining that the malls aren't open, not that people are dieing.
With a privately run health care system, it is going bankrupt and the work for this public health measure doesn't come with funding; US health care is paid for by elective surgeries and other low-value high-price stuff, not by a central government that can aim resources at public health prevention.
The individual state model doesn't work well, because if one state says "naughty word it, let them die", the states that don't do that have to shut off travel to those states or their work is for nothing.