Overwhelmingly, the historians rated this presidency as a political success, by which they meant that Mr. Bush has been remarkably able (or had been up to that point) to get initiatives passed through Congress, and he still had the support of about half the population. But that's not necessarily inconsistent with the presidency itself being a disaster. One can be successful at pursuit of something wrong, or evil, or misguided, or just plain stupid.
Ok, the left-ward leaning tendencies of the professoriate (statistically speaking) are well-known -or much-believed, anyway. But that turns out not to matter. Liberals weren't thrilled with George the Elder, either, and we certainly weren't crazy about Ronald Reagan, and yet the historians rated those presidencies as less disastrous than this one.
So why does an unscientific poll of such a small group matter? It's not hugely important, I have to concede. Yet, these are the people trained in evaluating long-term consequences of political leadership. Personally, they probably care as much about high gas prices and for the safety of a particular serviceman or woman as you and I do, but professionally they're trained to take the long view of leadership. And in the end, voters (rather than a subset of academically trained voters) decide the merits of any administration, and the voters could well disagree with these guys.
One unnamed (and thus I can't give credit, but I promise I didn't write this) historian said:
Indeed, Bush puts Nixon into a more favorable light. He has trashed the image and reputation of the United States throughout the world; he has offended many of our previously close allies; he has burdened future generations with incredible debt; he has created an unnecessary war to further his domestic political objectives; he has suborned the civil rights of our citizens; he has destroyed previous environmental efforts by government in favor of his coterie of exploiters; he has surrounded himself with a cabal of ideological adventurers . . . .That's why we should care.