Run to the extreme in the primary, move to the center in the fall: That’s expected. But moving from the cartoon world the Republican presidential candidates have constructed back into three dimensions might prove more difficult.

In their debate Wednesday night, the remaining candidates seemed to be continuing their drift from reality — the reality of a center-right electorate they propose to woo and govern, and of the complexities of the problems they promise to solve.

Take immigration. Early on, Ron Paul opposed building a border fence because it might be used to keep Americans in. When it comes to drifting from reality, he was ahead of the pack. But other candidates showed glimmers of understanding that real people are affected by this issue.

Rick Perry, you might recall, wondered if it made sense to bar promising youth, brought here as infants, from a college education. Newt Gingrich said that the United States wasn’t the kind of country to uproot from their communities millions of people who had lived here peacefully and productively for many years.

He soon began backpedaling, suggesting that it was only elderly grandparents he wouldn’t ship back to Mexico. And by Wednesday’s debate in Mesa, Ariz., the candidates had beaten any hint of nuance or compassion out of each other.

The former House speaker was ready to uproot not only immigrants but half of the Department of Homeland Security, too, sending Washington bureaucrats to the border, armed presumably with pistols and posthole diggers. Mitt Romney was citing Arizona’s draconian immigration law as a model; Rick Santorum was ingratiating himself with the state’s noxious Sheriff Joe Arpaio.

When CNN moderator John King raised the issue of contraception, you could sense that the candidates understood it was a trap — understood that, in the year 2012, most Americans do not understand why presidential hopefuls are debating the morality or legality of birth control.

But after trying to blame the media, they couldn’t keep themselves from tumbling yet again into a contraception debate disconnected from what most Americans are worrying about.

As Santorum clarified his view of birth control: “I think I was making it clear that, while I have a personal moral objection to it, even though I don’t support it, that I voted for bills that included it. And I made it very clear in subsequent interviews that I don’t — I don’t support that. I’ve never supported it, and — and have — and on an individual basis have voted against it. That’s why I proposed Title XX to counterbalance it.”

Okay.

Members of the audience tried to steer the candidates back to the real world. A man named Gilbert wanted to know what each would do about the federal debt.

No hard choices there, to hear the candidates tell it. “I’m going to go through every single program and ask if we can afford it,” Romney volunteered. Gingrich said he would save $500 billion a year by abolishing the civil service — which, he added later, would allow him to build the border fence for 10 percent of its projected cost. (Maybe the DHS employees will have to supply their own posthole diggers.)

Their view of the world beyond this country’s borders was similarly simplistic, verging on apocalyptic, with no acknowledgement of the difficult choices facing a president on, say, Syria.

Asked to briefly introduce himself, Santorum began this way: “I’m Rick Santorum. And we have a lot of troubles around the world, as you see, the Middle East in flames. . . .”

Romney, who not long ago was positioning himself as the Reaganesque, sunny champion of freedom, declared flatly, “The Arab Spring has become the Arab Winter.”

Gingrich — after choosing the word “cheerful” to describe himself in the debate’s lightning round — delivered this survey: “You live in a world of total warfare. . . . We live in an age when we have to genuinely worry about nuclear weapons going off in our own cities . . . . I believe this is the most dangerous president on national security grounds in American history.”

Poignantly, Santorum appealed from time to time for understanding that life isn’t all black and white. But it was the complexity of political life that troubled him, not the complexity of issues. To be good team players, Republicans sometimes have to support Republican-backed legislation they don’t approve of, he pleaded. Senators sometimes have to vote for big bills they don’t love in their entirety. Governing sometimes demands compromise (though he didn’t use the c-word).

Sadly for him, Pastor Paul was standing ready to refuse absolution. From his perch of thorough hypocrisy — Paul is a master earmarker who preserves his purity by voting against appropriations bills he knows will pass — the Texas congressman declared: “I don’t accept that form of government.”

And, of Santorum, “He is a fake.”

No, what’s fake is the two-dimensional canvas they’re presenting to voters.

fredhiatt@washpost.com