I was reading this article and shaking my head in disgust, when I had an epiphany.

Fifty-one percent of Democrats in the Economist-YouGov survey say they have a somewhat or very favorable view of the 43rd president, while 42 percent hold a somewhat or very unfavorable view of Bush.

I remember Dubya. He was, and still is, a war criminal. That hasn't changed. The only thing that has changed is liberals.
How can they forgive him?
To understand this, it requires a deep dive into tribal politics. Fortunately, this article does the hard work for me.

Party loyalists believe the gap between the two parties is huge. The Republican party is so egregiously horrible, they argue, that it is imperative to remain loyal to our only hope of stopping them: the Democratic party. This viewpoint is captured in a recent Democratic Campaign Coordinating Committee sign reading “Democrats 2018: I mean, have you seen the other guys?”
...Leftwingers, on the other hand, see the gap between Democrats and Republicans as smaller. They like to point out examples of silent bipartisanship: the complicity of Democrats in the disastrous war in Iraq and the racist war on drugs, for example, or the Obama administration’s continuation of Bush-era, corporate-driven education reform.
Behind this divide is a failure to see eye-to-eye over certain larger narratives – narratives that leftwingers talk about more than liberals do. The left often situates both parties within broader conceptual frameworks, such as neoliberalism, corporate power and imperialism. To defeat these larger, nefarious societal structures and historical trends, leftwingers argue, we must identify them and prepare a plan to conquer them – a task more difficult than just defeating the Republicans at the ballot box.
Many liberals, meanwhile, either have not thought about, do not believe in, or do not prioritise addressing these forces.

This is the critical point: liberals do not share my values.
Liberals don't care about our endless wars that slaughter innocent people and bankrupt the nation, just like Republicans.
Liberals don't care about wealth inequality because they believe in a capitalist meritocracy that doesn't exist, just like Republicans.
Oh sure, liberals give lip-service to leftist values, but then they forgive war criminals too. So who cares what they say?

Simply, liberals are as different from leftists as liberals are from conservatives.

So what do liberals value? The appearance of protecting minorities.
I say "the appearance" because liberals are delusional.

What’s more, the threat of Republican power, liberals point out, is especially acute to marginalised communities: whereas privileged idealists can afford to say “it has to get worse before it gets better,” immigrants at risk of deportation, black people at risk of police brutality and gay couples at risk of having their rights rolled back do not have the same luxury.

Which makes some sense, until you look at the track record (i.e. facts).
Let's start with "immigrants at risk of deportations".

Obama was the “deporter-in-chief” so you might think that liberals wouldn't like him.
Nope. Liberals are still in love with him.
Well, it's OK because Trump is so much worse to immigrants than Obama was, right?
Nope. Obama was, and is, still worse than Trump.

Mostly deportations have remained lower than in past years under the Obama administration. From January to June, Immigration and Customs Enforcement deported 61,370 criminals, down from 70,603 during the same period last year.

The same can be said about blacks, who are worse off under Obama.

There is no reconciling this huge gap between what liberals believe and value and reality.
What's more, pointing out these indisputable facts regarding immigration and the AA community on places like DKos will trigger unhinged fury and accusations of racism from liberals.
Why is that?
I used to think it was because of shameless, hypocritical, opportunistic, partisan politics. Now I think the reason is much deeper: Identity Politics.

Identity pertains not simply to the kind of person that we are. People have been sorted (and self-sorted) into kinds throughout history. Identity is different. First, it carries a determination about guilt or innocence that nothing can appreciably alter. Its guilt is guilt without atonement; its innocence is innocence without fault. No redemption is possible, but only a schema of never-ending debts and payments. Second, this schema is made possible because identity politics is, tacitly or expressly, a relationship — something quite different from sorting (and self-sorting) by kinds. In the identity-politics world, the further your distance from the epicenter of guilt, the more debt points you receive. What is the epicenter of guilt? Being a white male heterosexual. The debt points are not real currency, but they offer something that mere money cannot: a sense of moral superiority. “Join us,” says the Democratic party, “and though your actual wounds cannot be healed, or even eased, by our policies and programs, they can be covered with the cloak of righteousness.” This is the stuff of religion, not normal politics.

Hostility to contradictory facts and reality.
The delusion of moral superiority simply by inclusion in 'the club'.
Original Sin.
Blind loyalty to authority figures and institutions.
A child's-coloring-book knowledge of the real history of their basic tenets.
The inability of the leaders to accept responsibility for failures, and instead assigning the blame to a lack of faith and will in the little people.

You could just as easily be talking about a religious cult, or about the current state of liberal Identity Politics.

Of course, Republicans are no better, and in some ways are worse.
Like liberals, Republicans have their own "white version" of Identity Politics, with all of the same magical thinking, hostility to facts and logic, blind loyalty to authority figures, and of course a delusional reality.

The right, meanwhile, does not understand the divide, continuing to believe in a monolithic “radical left” filled with “radical liberals”. This leads to the funny situation, as one commentator noted, in which members of both the left and the right reach for the same “I made it through college without becoming a liberal” T-shirt.