Well, Amazon is something to consider. However, I think the big problem with Amazon is that they are actually taking packages out of the system now with their own delivery program. Fewer packages going through USPS reduces their profits.
The internet has also hit the USPS hard. How many first class letters have you mailed this year? Me, not too many and that is with me running a business. It used to be I'd have several catalog requests a week to deal with, plus most of the orders came by mail. Now, everyone just looks at my website or emails me. Many of the bills are now electronic delivery. Etc, etc. First Class letters used to be the main cash cow for USPS.
Then, we have the issue of the Universal Postal Union. That is where the various countries get together and decide how they will charge postage to each other. When I do the math on packages, it appears to me that the USPS is subsidizing a huge percentage of the packages coming into the country internationally. I'm talking about those things you can order straight from China for a buck or two delivered FREE to you in the US. Now, if I want to mail anything First Class Package up to about 4 ounces, it basically $3 and I have to use a discount service to get that price. So, if China is selling the item for $1 and it cost $3 to deliver just the US portion of the journey, somebody is paying the cost. And, that is the directly the USPS, and indirectly, USPS customers.
This disparity is current news if you google "Universal Postal Union News". The US was threatening to leave the union if there was not a deal. Looks like the union cut a deal to keep the US a member. Not sure how that will change prices. Looks like all those cheap, cheap direct from China deals will be hit next. That is actually fair, IMO. But, I suspect that it won't mean domestic shipping will drop any.