Indeed! They went through some hands in the primary also...
In the primary there is no real way of influencing anything by having just the party on the outside of the envelope.
In the general, though, many thousands of votes against Obama will be traveling through a series of hands, vulnerable to anyone of them who could take out “R” envelopes.
Postal workers are union, unions are typically very left... not that union members would EVER do anything unethical... And then you have college mailrooms, nursing home mailrooms, clerks in gated community offices, any place that handles outgoing mail, etc.
It’s scary to have this in PA where we are a large swing state in a critical presidential election against the most evil president our country has ever seen :-(