Well, I will only speak to St. Charles County, MO where I live, but I'm sure a lot of this is going to apply to what is going on throughout the US. Here is a chart of St. Charles County Cases:
Missouri stay at home order issued April 6th. Phase 1 Opening began on May 4th. All businesses open with social distancing adherence. I was eating out at restaurants from that day forward: No masks on patrons. Employees with masks. Seating every other table. Bars at the restaurants had stools two together spaced out. After about 3 weeks, the table spacing decreased and there were more stools at the bar. From May 4th on, my wife was attending her fitness classes. No masks at work.
Do you see a big spike from opening up? Me either.
But wait, what about phase 2 (no rules) looking like it caused the July spike. Phase 2 was pretty much a nothing burger because throughout May and early June the social distancing guidelines adherence at the restaurants I went to was decreasing and a lot of stuff was already operating as if it was Phase 2.
So, what caused this spike in cases? Well, Item 1 is extreme increase in testing.
So, you test more people, you're going to find more cases. But wait, the percent positive tests started ticking up also. So, something else is going on.
Throughout July, St. Charles County averaged 911 reported tests per day. So, I built the following chart to show the hypothetical cases based on the daily percent positive if they had been doing 911 tests per day since they started testing. (But wait you say, if they were doing more tests the percent positive would likely go down. I don't think so, because they were only testing symptomatic people early, but 50%-80% of the cases may be asymptomatic (see below) so, I think the percent positive may have increased even more because it is looking like the asymptomatic is closer to the 80% than the 50%). This chart takes the testing increase out of the equation and shows a truer picture of the "spread" of the virus.
So, that increase in late June and July is not normally how a viruses life cycle occurs in nature. So what is the cause of this "spike"? Item 2 on increased cases is the increased testing of people with no symptoms. It appears that asymptomatic individuals are a greater percent of infected individuals, so you more than doubled the pool of finding "cases" because you increased your odds of finding them.
This however doesn't explain all of it as lockdowns did disrupt one important vector of transmission - schools, especially colleges. Missouri closed schools in mid-March. So, as things started easing and people became more confident some of the spheres of friends that were cut off came back together giving the virus another go at susceptible individuals it didn't have access to before. That is why the average age of positive cases in July skewed heavily younger than the positive cases from March, April, and May. The other reason the positives skew younger is that younger people are more likely to be asymptomatic and they didn't really start testing people without symptoms heavily until late June and July.
Asymptomatic percentages: