President George W. Bush left office in January 2009 with some of the lowest poll numbers ever recorded. Nowhere were his policies more reviled than in foreign policy. U.S. global leadership had suffered severely during his administration, and voters, well aware of the damage to America’s reputation and the enormous addition to the national debt, handed the White House to the Democrats.

So why are so many of the candidates for the 2016 Republican presidential nomination rushing to revive the exact same Bush-era approach to international affairs?

The best case in point is the recently concluded Iran nuclear deal. The agreement blocks any path to an Iranian bomb, establishes unprecedented verification procedures, largely eliminates Iran’s enriched uranium and sharply curtails Tehran’s other nuclear research.

In the Bush administration, there was a definite preference for unilateral action — international cooperation was downplayed. The White House undertook the major foreign-policy gamble of the new century — invading Iraq — almost alone.

By contrast, President Barack Obama chose diplomacy with Iran to make clear to the world that such unilateralism had ended. His administration slowly and painstakingly built a sanctions regime that brought to bear the combined power of the world’s major economies and dozens of other countries. It was a slower, more methodical approach.

Though most now agree that “crippling sanctions” brought Iran to the negotiating table, many tend to gloss over the fact that it was diplomatic engagement — not unilateral action — that made the sanctions possible and produced the agreement. We should also not forget that many of the current opponents of the agreement strongly opposed the diplomatic effort to build that international consensus.

Yet leading Republican candidates are now struggling to outdo one another over who would abandon U.S. allies first. Wisconsin Governor Scott Walker has implied that military action might be required on “Day One” of his presidency. Former Florida Governor Jeb Bush has implied that it might take a little longer. There’s little sign that either of them realize the critical importance of Washington leading an international effort.

And if U.S. allies are of little importance to these candidates, international institutions like the United Nations International Atomic Energy Agency appear to be held in even lower esteem. In denouncing the pact with Iran, despite its unprecedented verification and enforcement provisions, several candidates declared their outrage over the fact that the atomic energy agency was responsible for the details of inspections. Given that the agreement was successfully negotiated by all the permanent members of the United Nations Security Council, it was expected that critical enforcement of the agreement would be managed by the atomic energy agency.

All this brings to mind George W. Bush’s similar dismissal of existing international institutions. For example, when the head of the U.N. inspectors in Iraq, Hans Blix, reported in early 2003 that he had doubts about the presence of weapons of mass destruction there, and that, in any event, a few more months of inspections would settle the issue, Bush disregarded his counsel and invaded Iraq. We all know now that there were no WMD in Iraq.

In stark contrast to that foreign-policy disaster, the Iran agreement has the unanimous support of the Security Council, as well as backing from major economic powers, including Germany, India and Japan. This week, the Gulf Cooperation Council, which includes Saudi Arabia, Bahrain, Kuwait, Oman, Qatar and the United Arab Emirates, joined Egypt in fully endorsing the deal.

The value of this global support is immeasurable. It is a force multiplier of enormous consequence. By contrast, if the deal is abandoned, and the United States finds itself moving toward war with Iran, Washington should expect to fight that war alone. Even if America does not bomb or invade Iran, it would still be a pariah because the other countries will resume relations without Washington — again relegating the United States to lower status in the world.

For decades, the Republican Party — my party — was widely viewed as a party of wise and thoughtful national-security leadership. That brand was severely damaged by the Bush administration. It now appears that the field of Republican presidential candidates is looking to make that damage permanent.