That was already expected though. In the qualifiers for the women's 100m the best American placed 8th, in the 4x400 they placed 3rd, so getting 3rd again in the finals isn't over or under achieving, and in men's discus qualifiers the highest placed American barely made the top 10. In all 3 events they performed about as expected, no better or worse.
Today, they have an ok shot at medaling in the men's high jump with JuVaughn Harrison tying for 4th place in the heats and in men's 100m Fred Kerley is 3rd in qualifiers so there's an opportunity there too. In women's triple jump they are in 11th so don't expect them to medal, and in women's shot put China is #1 and #2 (!!!) but Raven Saunders of the US is in #3 and only .01 below #2 Jiayuan Song.
So yea, tomorrow they have a decent shot at getting some medals, but they would be overachieving if they get a single gold in any of the athletics events. In fact, China has a higher chance of getting a gold today in athletics (women's shot put) than US has in any of the athletics medal events. So watch out for China in women's shot put in a couple hours!
For the rest of today America has a lot of chances at medaling or getting gold it's true, but China also has a few it's expected to win. China has women's badminton where China is competing for both gold and bronze (no US competition) and women's 3 meter springboard where China is #1 and #2 so hoping for a gold and silver.
US of course has an insane amount of events to medal or place first in today but none of them are athletics. I've looked into each event and there's quite a few:
US has men's BMX freestyle where they have two athletes but both placed last in qualifiers (but one of those was due to unlucky crashes so they may yet medal still), women's BMX freestyle where both US athletes placed #1 and #2 in a dominant fashion so they are likely to get a gold and silver, men's team foil where they are in the quarter-finals but not sure if they'll do better than bronze, men's golf where they might actually get gold (American Xander Schauffele has been leading by only 1 stroke but consistently so), in women's uneven bars Sunisa Lee only placed second so no guarantee of a gold but definitely going to medal outside of a rare occurrence (two Chinese qualified as well but only in 7th and 9th), in women's vault Simone Biles was dominant but she pulled out so being replaced by MyKayla Skinner (who was in 4th place) and Jade Carey expected to gold as she was #2 in qualifiers behind Biles (she has competition from the Brazilian though). And of course swimming where Caleb Dressel of the US will definitely place #1 and get the gold in men's 50m freestyle, in men's 1500m freestyle Robert Fink has a good chance of medaling and placed #2 in heats, and women's 4x100m freestyle looks very close for the US but could be photo finish between 1st place and 4th place.
Outside shots for both China and the US in today's events include men's floor where US and China are 7th and 8th respectively, men's pommel horse where US and China are 4th and 6th (though 4th place American did quite a bit better than the Chinese in qualifiers), and in men's 4x100m freestyle where China might have a better chance of medaling than the US but we'll see. China placed 4th but US barely qualified, placing 7th, but the times are fairly close to each other so it might be a crapshoot. Lastly women's 50m freestyle is also likely a crapshoot, with the American and Chinese competitors qualifying but not placing well (still the times are fairly close).
First medal event is just starting, we will see if Xander Schauffele of the US can maintain his lead in men's golf.