The timing doesn't line up - the USPS has been under attack since well before 2017. This reason might be reinforcement, but it can't be part of the core rationale.

And, honestly, there are "politicalish" scandals like this pretty frequently - I don't know if you recall the uproar about the IRS targeting conservative groups a few years back[1].

1. Which was, for clarity, disproven after the fact https://en.wikipedia.org/wiki/IRS_targeting_controversy

...by giving 97 workers union time off to perform political activities. It seems like a petty reason to trash an organization that receives no taxpayer funding, and punish the millions of poor and rural Americans that depend on it.