I just caught a moment of Harball and saw Chris Matthews criticizing Trump for taking a “blame everything on Obama” approach. Pretty sure he never criticized Obama for taking the “blame everything on Bush” approach for almost his entire presidency.
I think part of the issue is that Obama’s policies were often criticized not directly, but by using oddly specific made-up statistics. By arguing with those imaginary statistics (but not the implied policy criticism), it often ended up making that implied criticism point back to a point in time prior to the Obama administration, whether or not the implied criticism was ever valid in the first place.
For example, RW pundits often said Obama decided to pull out of Iraq too fast, and Obama correctly stated that the pullout timetable was negotiated and finalized by the Bush administration. Does that absolve him entirely of the conditions in Iraq post-pullout? Not at all. Does it mean that the conditions in Iraq were determined by the pullout timetable? It doesn’t really address that part of the question at all. But the pullout itself was absolutely, positively, not his call. By arguing with the made-up statistic, however, he avoided talking about the conditions in Iraq, and also didn’t have to address if the timetable was related to the conditions there. Intentional? Maybe. But I think it falls more on the side of “correcting the record” than “shifting the blame”, when you’re responding to something that’s factually inaccurate to begin with.
Similarly there was a common refrain that Obama created ISIS, which was equally impossible given that it happened before Obama. Does that absolve him of any blame for ISIS-related failures? Not at all, just the creation of it.
Similarly, RW pundits often said that 75 straight months of job growth was impossible, that the feds were fudging the statistics, and the economy was weak. Obama correctly pointed out that the numbers were calculated the same way they always were, and that you can have 75 straight months of job growth and still have a weak economy if you’re starting out from a position of extraordinary weakness 75 months ago, which did in fact exist.
I think the difference here is that, if a criticism is missing the made-up statistics, you can’t dodge or deflect the issue by arguing with the made-up statistics (well, I suppose you could try to argue with reality, but that tends to be obvious). I’m sure there was some blame-shifting under Obama, but at least as far as I can remember, it was much more canny and could certainly be interpreted, much of the time, as simply correcting the record.