Can you travel in the USA without renting a car?
Yes, but only in the right USA. New York, Washington DC, Boston, Chicago and some city corridors can work well without a car; national parks, beaches and small-town routes usually become awkward fast.
Answer
The USA is not one transport system. In a few cities, a car is a burden: parking is expensive, traffic is slow and transit or walking makes the day easier. In many other places, the car is the trip. It unlocks park trailheads, beach towns, suburban hotels, scenic roads, family stops and the ability to change plans when weather moves in. A car-free USA trip is strongest when you design it deliberately, not when you hope gaps will solve themselves. The Northeast corridor, New York-focused travel and some major city combinations can be excellent without wheels. A national parks road trip without a car is possible in pockets, but the logistics become the main character.