Yes, I think he should, but not because Bush isn’t guilty.
Face it, Bush isn’t going to be held accountable for what he’s done. Most likely, neither is Cheney or Yoo or anyone else who should be. As soon as a newly-elected Obama tries to start investigating the old administration, the GOP will start howling and saying things like “we need to focus on the future and move on” (i.e. the huge task of fixing the mess the Bush presidency has left us.)
And it’s true, Obama needs to focus on fixing the economy and the host of other important issues, and not distract the media and the country with an epic investigation. But why pardon Bush?
Because realistically the alternative is to do nothing. Because it’s a quick, sure way to move on, yet still acknowledging that crimes were committed and that Bush’s actions were (in an ideal, apolitical world where we had the luxury of justice) egregious enough to require either a pardon — or prosecution. After all, why would Obama pardon Bush unless he felt Bush needed pardoning?
It would be a stain to Bush’s legacy only, but that would allow a bipartisan investigation of the particulars of the Bush administration’s actions to take place, and it’s important that happens. It would allow the country to move forward on other issues, while noting for posterity that trying to achieve an Imperial Presidency, as exemplified by Bush and Nixon, always results in offenses needing a pardon.