In a blog post guaranteed to tick off members of both parties, Daniel Mitchell tries a first approximation of where the blame should be assigned:
Well, it turns out that Social Security is a relatively minor part of the problem, so even though President Roosevelt’s policies exacerbated and extended the Great Depression, the program he created is only responsible for a small share of the fiscal crisis. To give the illusion of scientific exactitude, let’s assign FDR 13.2 percent of the blame.
The health care numbers are much harder to disentangle because it’s not apparent how much of the increase is due to Medicare, Medicaid, Bush’s prescription drug entitlement, and Obamacare. A healthcare policy wonk may know these numbers, but the CBO long-run forecast didn’t provide much detail.
So with a big caveat that these are just wild estimations, I feel reasonably comfortable in saying that both Bush and Obama made matters worse with their reckless entitlement expansions, but that they merely deepened a fiscal hole that was created when President Johnson imposed Medicare and Medicaid.