Good grief, if the Democrats are stupid enough to run on George W. Bush again in the fall, and if the Republicans are too incompetent to successfully ignore it, then the nation pretty much deserves what we get.
Here we have a party that took power in 2006, including Senators Barack Obama, Joe Biden, and Hillary Clinton, still calling out Bush for "failed policies of the past" instead of talking up their successful policies of the present. Voters are upset about the direction of the country--bad policies, illegal immigration, no jobs, too much debt and a war we can't finish. They don't want to hear about Dubya anymore. The GOP needs to keep hitting on what matters. Falling into defending Bush will lead nowhere, which is why they're trying it.
If recent primary elections here in left Tennessee are any indication (the four-term ex mayor of Memphis, running on a race card platform, was crushed in the 9th district Dem primary by Steve Cohen, which likely means base turnout was low) the momentum is there.
BTW, the Dems are giddy that parts of Bush's memoir might leak before the election, setting up their MSM friends to focus on the past and hence their tactic, but what if the leak is a bombshell that helps the GOP? Something as yet untold, for example? Every book has a hook.