The race for the White House is a lop-sided affair, with 16 Republican candidates facing Hilary Clinton and four other Democrats. Tom Switzer writes that Republican policy on the Iraq War has taken the party back to 2002.

A couple of months ago Jeb Bush – a leading Republican presidential candidate and son and brother of former presidents George Bush – dug himself in a political hole. Appearing on the Fox News Channel, he was asked whether he would have launched the 2003 invasion of Iraq, knowing what he knows now. He answered a different question – whether he would have authorised regime change based on the intelligence at the time. “I would have,” the former Florida governor replied, “and so would have almost everybody that was confronted with the intelligence they got.”

The following day, given another attempt to answer the hypothetical question, Bush remained at a loss to explain his position clearly. “The simple fact was, look, mistakes were made, as they always are in life… and foreign policy,” he suggested. He also argued that “going back in time and talking about hypotheticals” was a “disservice” to those who served in Iraq.

By the end of the week, after his vacillating and incoherent position had been subjected to intense criticism from all and sundry — including his rivals for the Republican party’s presidential nomination — Bush conceded he “would not have gone into Iraq.” But he added the world is “significantly safer” because his brother did go into Iraq.

The episode raised questions not just about Bush’s preparedness as a serious candidate for high office. (Surely his campaign team should have been prepared for the inevitable question, given that, among other things, it was Jeb’s brother who launched the invasion.) But the episode brings to mind an untold truth in Washington: the Iraq war is the spectre that haunts the Republican Party.

Here was a leading Republican presidential candidate comprehensively failing to recognise what the eminent historian Tony Judt called “the worst foreign policy error in American history” – one that could not simply be blamed on flawed intelligence or lousy execution.

Think about the implausible justifications for the war (weapons of mass destruction, al-Qaeda links, human rights), or the costs in blood (at least 200,000 Iraqis and 5000 coalition troops) and treasure (more than $1.5 trillion), or the deaths and exodus of most of Iraq’s Christian community, or the tarnished image of the U.S. in the torture rooms of Abu Ghraib and the CIA’s secret prisons, or America’s dissipating prestige and Iran’s enhanced power in the region, or the widespread view among foreign-policy realists at the time that any threat Saddam Hussein posed justified containment and deterrence, not preventive war and regime change. No wonder polls show a clear majority of the American people say the invasion was not worth it.

And yet most American conservative pundits and Republican politicians, including Jeb Bush himself and the other – at last count — fifteen candidates (save one) continue to blame President Obama for the mayhem in Iraq that has culminated in the rise of Islamic State.

The argument goes like this: the “premature” withdrawal of all American troops in December 2011 – a deadline, incidentally, that George W. Bush himself had put in place in 2008 – reignited all those sectarian tensions that the so-called “surge” of U.S. forces had bottled up in 2007.

In reality, the taproot of today’s crisis in Iraq was the invasion itself. With the downfall of a Sunni regime, the majority Shiite became the new winners in post-Saddam Iraq; and the minority Sunnis the new losers. The former turned to their Shiite brethren in Tehran for support; the latter turned to a Sunni insurgency that has morphed into a plethora of Sunni jihadists, including the Islamic State. The inevitable withdrawal of U.S. troops simply reignited those age-old demons that the invasion unleashed in 2003.

The result: a simmering cauldron of sectarian malevolence that has not just broken up Iraq as the world has known it since the collapse of the Ottoman Empire a century ago. It could also lead to a broader regional showdown between a Saudi-led bloc and a rival alliance led by Iran’s Ayatollahs.

This history is important in understanding the problem that afflicts today’s Republican Party. For much of his presidency, Obama has tried to redefine the U.S. role in the world in a way that reflects more limited resources and changing circumstances of the post-Iraq war era. His political opponents, with rare exceptions, are talking as if it’s 2002.

After the attacks of September 11, 2001, the fundamental assumptions behind Bush administration foreign policy was that global problems should be solved by force in a world divided into good guys and bad guys, and that the U.S. had a special mission to lead globally. “America is an empire now,” Senior Bush adviser Karl Rove boasted in August 2002, “and when we act we create our own reality.”

That mindset prevails in today’s GOP. It’s not so much a neo-conservative worldview: the notion that the U.S. has a special mission to transform the world in a more democratic image. It has more to do with what James Lindsay of the New York-based Council on Foreign Relations’ calls “assertive nationalism”: the belief that compromise is never possible with America’s foreign enemies and that Washington should use U.S. military power to defeat threats to U.S. security (broadly defined).

Take the Republican Party’s hostile response to the Iranian nuclear deal struck this month. “This is the greatest appeasement since Chamberlain gave Czechoslovakia to Hitler,” warned Senator Mark Kirk, referring to the gullible British leader who signed a peace accord with the Nazi dictator in 1938. Presidential candidates piled on: “one of America’s worst diplomatic failures” (Scott Walker), “a fundamental betrayal of the security of the United States” (Ted Cruz), “dangerous, deeply flawed and short sighted” (Jeb Bush) and “one of the most destructive foreign policy decisions in my lifetime” (Rick Perry), and so on.

Never mind, as the Iraq war made painfully clear, America’s limited power to make adversaries conform to its expectations. Never mind, too, that a Pax Americana is incompatible with a domestic conservative agenda of spending cuts, small government and balanced budgets. Although the U.S. possesses the military means to defeat any other country, there is not an American solution to every problem. In fact, there are a good many international problems for which there may be no solution at all.

That is what Rand Paul has argued in recent years. “We need a foreign policy that recognises our limits and preserves our might,” he told the Centre for the National Interest last October. The first-term Kentucky Senator is the only presidential candidate to challenge the hawkish wing of the GOP. And his call for a more prudent, cautious and discriminating foreign policy fits the moderate Republican tradition of Dwight Eisenhower, Richard Nixon and George HW Bush.

“If you insist on unconditional surrender as a prerequisite to diplomacy, there will be very little diplomacy,” Paul argues. For mouthing such self-evident truths of international relations, Paul has been disowned by many Republicans and has even been denounced as an isolationist and appeaser by fellow conservatives. But this is what Republicans should be saying, coherently and confidently, lest they find themselves digging in another hole that damages both their own interests and those of the United States.

Tom Switzer is a research associate at the University of Sydney’s United States Studies Centre and host of Between the Lines on the ABC’s Radio National. This article can be republished with attribution under a Creative Commons Licence.