We could use all renewables. It would take a shift in our energy usage habits, but it's very obtainable.

Even things like properly insulating all homes would be massive, making it so the vast, vast majority of US homes would not need heating at night to stay comfortable.

Really all that would need constant power is refrigeration, creature comforts, and emergency services. This is obtainable with different energy storage methods, and If we hold to capitalism, increasing electric rates in the evening.

Yes, there are countless exceptions, but they are in the minority and we can adjust to them.

Yes, nuclear is an option to, but it should be a stopgap for now to go renewable. Fission might come, it might not. Plan for what we have, not what might be.