The strongest claim Democrats can make about their opponents is that they would return the country to George W. Bush's policies. The tact has two benefits. First, it drives public opinion extremely well:

Which brings us to the main reason that Third Way, a centrist Democratic group, organized this breakfast discussion, which was to unveil a poll done by the Benenson Group (Joel Benenson is Obama’s pollster). Its central finding is the potency of Bush as a negative for the Republicans if the Democrats can find a way to reinject him into the campaign. That’s the good news. The bad news, says Matt Bennett with Third Way, “Republicans have done a spectacular job of removing the albatross of Bush.” When asked if the GOP would return to Bush policies if they gain control of the Congress, even Democrats said no, surely Republicans wouldn’t be that stupid. 
But when Bush’s name is tied to the economic ideas that conservatives are promoting, and they are identical, there is a 49-point swing in favor of Obama, the biggest swing Bennett said he’s ever seen in a poll.

Second, it's completely true. Even when Republicans claim they have new ideas, those ideas consist of undoing President Obama's agenda and thus returning to the Bush-era status quo. The only Obama policy that has drawn any Republican support is his continuation of Bush-era foreign policies.

Democrats' attempt to tie Republicans to Bush-era policies is being analyzed entirely in political terms. But it's worth considering as an actual analysis as well.