Jonathan Martin suggests that Romney would benefit by opposing the records of both Bush and Obama:

Indicting both parties for America’s fiscal problems would help Romney detach himself from Bush and buy a measure of credibility with voters fed up with Washington. And given the remorse many conservatives have about the spending that took place under the last administration and the GOP base’s immense desire to oust Obama, it seems unlikely that Romney would lose many Republican loyalists in the course of trying to appeal to swing voters.

Martin underestimates how badly many Republicans would react to an acknowledgment by Romney that Bush-era policies are responsible for a large part of the debt. There are several reasons why Romney is not likely to do this, and perhaps the most important of them is that Romney and his advisers may not fault Bush for the debt added by his policies. If Romney has chosen not to indict Bush for his failures, perhaps that is because he doesn’t recognize them as failures. If Romney has evidently learned little or nothing from Bush’s foreign policy failures, why would it be any different on fiscal matters?

The official story is that the presence of Paul Ryan on the ticket demonstrates that Romney has learned something from the experience of the Bush era, but that makes sense only if we forget that Ryan was a reliable supporter of every deficit-expanding bill that the House voted on. To indict both parties for fiscal irresponsibility is to remind the public that Ryan was part of the problem during the Bush years. That hardly inspires confidence that a future Romney administration would be any more fiscally responsible than the last Republican in office. Besides, it’s not as if Romney is in any position to criticize Bush-era Republicans for their fiscal irresponsibility, since he has said in the past that he supported the Iraq war and Medicare Part D. He can’t break with Bush-era Republicans because he was one of them. Finally, it’s simply too late at this point for Romney to separate himself from the Bush legacy that he has never once addressed in this campaign. Romney is losing in part because most voters remember just how badly his party failed when in power. He can’t “buy credibility” now with a belated admission of his party’s failures.

P.S. One more reason that the Romney campaign won’t do this is that they’re oblivious to the damage Bush’s record is doing to them. As Martin writes later in the story:

Romney’s campaign, while not ruling out the possibility of taking on both parties, indicated that they don’t feel haunted by the ghost of Dubya.