Most theories for why the president came unglued like a papier-mache doll in a steam bath during his press conference this week center on the fact that he can’t stand having his liberal bona fides questioned.

When Iran unveils its nuclear program or slaughters dissidents in the streets of Tehran, Barack Obama keeps a steadier hand than G. Gordon Liddy’s over a candle. Question his citizenship, his patriotism, even his jump shot, and he’s all Vulcan poise. But if you doubt his commitment to The Cause, he turns into Charlie Sheen without his Ritalin.

There are other theories, of course. He was just pretending to be mad so he could seem more moderate as he preps his 2012 bid for re-election. He hates giving Republicans what they want. Obama’s “political immaturity,” as South Carolina Sen. Lindsey Graham said in an interview with National Review Online, leads to “whining” when he can’t have his way.

All of these theories are possible, and none of them are mutually exclusive. But there’s one more possible reason for his dyspepsia. This week Obama lost his argument with Hillary Clinton.

It’s largely forgotten now, but during their lengthy primary battle, the two committed liberals’ greatest disagreement wasn’t over policy or their shared disdain for George W. Bush. It was over their different visions of the presidency.

For example, in a Nevada debate, Obama admitted that he wasn’t a particularly organized person. But that was OK because the core role of the president shouldn’t be organizational but inspirational. “It involves having a vision for where the country needs to go … and then being able to mobilize and inspire the American people to get behind that agenda for change.”

Pshaw, responded Hillary, the president is really a “chief executive officer” who must be “able to manage and run the bureaucracy.”

This disagreement was symbolized by their respective role models. Obama likened himself to Martin Luther King Jr. and John F. Kennedy, inspirational leaders who led through rhetoric. Clinton sided with Lyndon Johnson, the guy who spun the shining words into actual legislation and got it passed, often on a bipartisan basis.

The debate played itself out by proxy in liberal magazines and in snippets of speeches and short outbursts on the stump, with most liberals siding with Obama over Clinton. Some even suggested she was a racist – or at least race-baiting – for daring to suggest that all he offered was the ability to give a good speech.

But even some of Obama’s biggest fans admitted that his devotion to the magical power of words stemmed from the fact that he had little else going for him. “Barack Obama could not run his campaign for the presidency based on political accomplishment or on the heroic service of his youth,” David Remnick wrote in the New Yorker after Obama won the general election. “His record was too slight. His Democratic and Republican opponents were right: he ran largely on language, on the expression of a country’s potential and the self-expression of a complicated man who could reflect and lead that country.”

Fast-forward to this week. Obama’s undisciplined diatribe against the “purists” in his own party who oppose compromise amounted to an abject admission that Hillary was right all along.

“Measuring success” by the no-compromise standard, Obama declared, means “we will never get anything done. People will have the satisfaction of having a purist position and no victories for the American people. And we will be able to feel good about ourselves and sanctimonious about how pure our intentions are.” But, he suggested, liberals will make little progress.

Obama then went on a stem-winder about how “this is a big, diverse country. Not everybody agrees with us. I know that shocks people. The New York Times editorial page does not permeate across all of America.”

All true. And the Democrats are being foolishly purist, as we saw Thursday when House Democrats voted to reject the tax compromise.

But denouncing purists and accepting that significant swaths of America aren’t going to be persuaded by your rhetoric is an admission that the Obama vision of the presidency either doesn’t work or that Obama isn’t up to the job of making it work.

Indeed, even on health-care reform, his signature accomplishment, Obama failed to mobilize and inspire the American people to his side. He got that passed with LBJ-like legislative skullduggery and sleight of hand, not “yes we can!” rhetoric.

Admitting you’re wrong is part of growing up, and growing up can be painful. At least it certainly looked painful watching it on TV.

© 2010 Tribune Media Services, Inc.