If a hospital is overrun, substandard care will always occur, mainly because you won't be able to get the ancillary services and testing patients need in a timely fashion. You can't just snap your fingers and grow another CT scanner and the techs needed to staff it, for example. This has a knock-off effect of delaying discharges, which further exacerbate capacity issues, and the invitable complications that start to accumulate (DVTs, falls, nosocomial infection, etc.) the longer a patient stays in the hospital.
Maybe someone can correct me if I'm wrong, but the US gov't never closed the ports and the borders remained open to trade (I still see just as many Canadian-registered tractor trailers here in northern Vermont as always, but now rarely see cars with Canadian plates). But I seem to recall the port of Long Beach suffering huge backlogs after a COVID outbreak amongst the port workers. I believe this was before the vaccines were authorized, but if an insufficient number of the workers get vaccinated, it could easily happen again.