Liberals and even Libertarians love this tactic: When conservatives attack Obama's irresponsible spending, talk about Bush's irresponsible spending. It genuinely misses the point: Republicanism and Conservatism aren't synonyms. It's a straw man argument.
Look, most conservatives are also registered Republicans, especially in elected office. But it's not a dual enthymeme. While most conservatives are Republicans, most Republicans aren't conservatives. (For those of you from Palm Beach County, FL, it's kind of like: all bears are mammals, but all mammals are not bears.)
This brings us to former President George W. Bush. I've defended President Bush and I continue to do so, primarily on the grounds of National Security. (I've said for years that Bush was a good President because a) we had no major Al Qaeda attacks on American soil post 9-11 and b) while he was President, Iran and North Korea sat in their corners and played with their blocks quietly.) Furthermore, if you told me I could trade Obama for Bush, I would literally knock people over to get a pen so I could sign that paper, toot-sweet.
That being said, on economics, Bush in many ways governed less conservatively than Bill Clinton. (Gasp!) Let's not kid ourselves, Clinton was a weather vane. If the population wanted him to govern according to the platform of the Fancy Dress Party, he would have. (It's a real thing, look it up!) He also quietly instilled a lot of liberal policies and nominated many liberal judges. Oh, and let's not forget that the conservative reforms of Clinton were forced upon him by Newt Gingrich and the Republican Revolution. I've always said the 90s boom was not due to anything Clinton did but due to policies Clinton fought and lost then took credit for, like Welfare Reform and the Capital Gains tax cuts.
With the exception of Bush's tax rate reductions (they've been in place eleven years, I refuse to call them "tax cuts"), Bush put forward a lot of big government policies. Medicare Part D is one of the biggest examples. No Child Left Behind is another. (Granted, this would've had a better chance of succeeding if schools didn't do their darndest to circumvent that law instead of following it.)
Either way, Bush did not overall govern as a conservative. One cannot consider Bush's failures as an indictment of conservatism. As far as Ronald Reagan, liberals hate to remember that Reagan got as much done as he did with a Democratic House of Representatives blocking him every step of the way and a Democrat Senate during his second term, and when he had the Senate he did not have a majority sufficient to override a philibuster. So when you think about it, the levels of conservative reform Reagan accomplished were darn near miraculous.
At the end of the day, Bush was an example of the failure of REPUBLICANISM but not conservatism, and that failure was primarily because Republicans stopped governing as conservatives. And that's why there's a Tea Party, friends. To get conservatism back into the GOP.