Citation needed that conservatives killed USPS. I didn't find any unbiased sources to confirm this. To the contrary, the 2006 bill was a bipartisan measure passed by voice vote in the House and unanimous consent in the Senate.[1]
While that's true, it doesn't appear to have been a partisan or even controversial bill at the time, so I feel that it's disingenuous to blame Republicans.
If you control the majority of a legislative body, I argue it’s reasonable to blame that party for legislation they pass (as they could just as easily not pass it with the control they have). Likewise, the Republican President could have vetoed it (which he did not do).
Also, the legislation was sponsored by a Republican (Thomas “Tom” Davis III
Sponsor. Representative for Virginia's 11th congressional district).
And the other party, which came into power just two years later also "could just as easily" have repealed it. So you must blame the other party as well in this case.
[1] https://www.govtrack.us/congress/bills/109/hr6407