I don’t even think you could call it propaganda. Libs basically psy-opped themselves, organically, from the grassroots, with their intense emotional need to believe Trump was the worst president by every possible metric. The moment Bush criticized Trump, they were ready to welcome him back.
Couple that with the facts that (1) their saint Obama did much of the same stuff Bush did and they were forced to retroactively justify or downplay it as no big deal, and (2) libs are mostly not actually doves and only opposed the Iraq War retroactively because it was a failure not because it was fundamentally wrong and immoral—and it became the only logical conclusion for most libs that Bush was actually not that bad.
I’d be open to an argument that the fake astroturfed movement of “NeverTrump conservatives” (which are purely a Washington faction, with no actual constituency in the population) could qualify as propaganda that produced this, but I would say that mainly this represents the libs themselves’ sincere and organic beliefs. MSNBC follows what they want to hear, it doesn’t dictate their opinions to them, they dictate the scripts to MSNBC.