President Obama’s effort to discredit Mitt Romney as a credible economic repairman has several elements: using his business career to cast doubts on his desire to help the middle class, tying him to the radical proposals of the Paul Ryan budget, and — something hinted at in Obama’s recent minute-long, talking-to-the-camera ad — portraying his plan as a mere reprisal of the failed George W. Bush approach.

Last night, Brian Williams asked Romney to distinguish his approach to economic growth from Bush’s. The answer was a mere recapitulation of his plans (“Well, let me describe — actually, there are five things that I believe are necessary to get this economy going … ”). I won’t reprint the entire answer, but Romney did not make the slightest attempt to distinguish his approach from Bush’s. Of course that is because it’s the same thing! Every single idea Romney listed — low taxes, free trade, less regulation, developing energy, etc. — was part of Bush’s program.

Now, the usual Republican answer here, on how their approach will succeed where Bush’s failed, is to shout, spending! Romney promises to cut it. Bush also promised to cut it, but didn’t. I don’t think this really answers the main objection — lower spending may help the long-term budget picture, but the policies Republicans most directly associate with economic growth are taxes, regulation, and energy. And here Romney really is proposing the exact same policies as Bush.

But the surprising thing is that Romney didn’t even have that, or any other handy answer to the question. This is a pretty bad political messaging slip-up, but it also indicates a larger problem: Republicans haven’t really internalized the degree to which Bush’s policies truly failed to produce strong economic growth. They blame him for letting spending grow too high, and they recognize that the crash was a bad thing, but conservative rhetoric almost uniformly fails to acknowledge that even pre-crash growth under Bush was absolutely miserable.

And so conservatives have engaged in no critical examination whatsoever of their belief that the combination of low marginal taxes, lax regulation, free trade, and drill-here-drill-now will necessarily result in rapid growth. Which is why, unlike Obama’s appeal to economic nationalism, his attempt to tie Romney to Bushonomics is actually a persuasive rebuttal as well as a politically potent one.