My washing machine drain is backing up. I've used chemical drain cleaners without success. I rented a hand held power snake, but it only got as far as the
p-trap and wouldn't bend around the curve to get at the stoppage. I feel the
Stoppage is beyond the p-trap because of the time it takes for the water to back
Up. The p-trap appears to be brass and the connecting pipes are copper.
I tried to heat up the brass connections to be able to remove the p-trap, but
Was unable to loosen the fittings. How do I get past the p-trap with a snake, etc.

The fact that you tell me you have a brass trap and copper standpipe tells me that you probably have a inch and a half washer drainage system. Did the washer ever drank directly if or is this a new problem? You may rent a power snake and snake from the washer roof vent. However, if there is still a problem after snaking the roof vent. Get back to me and I will give your solution. Good luck, Tom