When transferring from an international to a domestic flight at Newark Liberty Airport, does one need to retrieve checked bags?

When transferring from an international to a domestic flight at Newark Liberty Airport, does one need to retrieve checked bags? - 1

You must take them thru Customs.

Yes. You go through Immigrations, get your bag, go through Customs, then drop it off at the re-check station.

That depends on where the flight comes from. There are a few places like Canadian airports, where you pre-clear US passport control and customs before you get on your initial flight. For those, you don't have to clear immigration or customs when you get to the US. For most international flights you do have to go through both passport control and customs in Newark. In that case, you do pick up checked bags as a part of clearing customs. When you get through customs you drop your bags off to be sent to the connecting flight. They will already be checked to your final destination.

Yes. For Customs.

When arriving in the USA you have to take your luggage through customs and then hand it in again for your domestic flight