President George W. Bush declarese the end of major combat in Iraq as he speaks aboard the aircraft carrier USS Abraham Lincoln in May 2003. The subsequent long struggle in Iraq looms over the 2016 presidential field. (J. Scott Applewhite/AP)

Seven years after he left office and with his brother now running to succeed him, George W. Bush in many respects remained the most important Bush on the Republican debate stage this week.

The legacy of Bush’s badly managed and still largely unpopular war in Iraq — and the broader strategy of foreign regime change it represented — hovered over the deep foreign policy disputes that emerged in the fifth GOP presidential debate.

While the candidates ramped up their increasingly forceful rhetoric on national security issues, their overall tone masked fundamental disagreements over American military interventions abroad.

Terrorism and war were the exclusive focus of the Las Vegas debate, the first since attacks in Paris and San Bernardino, Calif. The most significant division among the candidates concerned the merits of military interventions in the Middle East since the 9/11 attacks, including Bush’s invasion and occupation of Iraq.

epublican presidential candidates Donald Trump and Sen. Ted Cruz (R-Texas), shown here at Tuesday’s GOP debate in Las Vegas, are both criticial of past U.S. interventions to topple dictators. (Ethan Miller/Getty Images)

On one end were candidates such as former Florida governor Jeb Bush and Sen. Marco Rubio (Fla.), who say the United States has a moral and pragmatic obligation to maintain a forceful presence abroad. But rivals such as business mogul Donald Trump and Sen. Rand Paul (Ky.) have condemned past interventions in the Middle East, with little distinction between military efforts led by George W. Bush and those led by President Obama. Trump has made his onetime opposition to Bush’s war in Iraq a central part of his foreign policy credentials.

“We have done a tremendous disservice, not only to the Middle East — we’ve done a tremendous disservice to humanity,” Trump said at Tuesday’s debate. “The people that have been killed, the people that have [been] wiped away, and for what? It’s not like we had victory.”

Paul, the libertarian-leaning candidate, explicitly blasted Republicans — including several candidates on the stage — for supporting many foreign interventions.

“The vast majority of those on the stage want . . . regime change. They want it in Syria. They wanted it in Iraq. They want it in Libya. It has not worked,” Paul said. “Out of regime change you get chaos. From the chaos you have seen repeatedly the rise of radical Islam.”

For Jeb Bush, the problem of his brother’s legacy has been particularly inescapable.

He fumbled a question about the war in May, first indicating he would still have supported his brother’s invasion of Iraq even knowing that there would be no weapons of mass destruction. He then said he had “misunderstood” the question and dismissed it as a “hypothetical” before finally saying he would not have approved the invasion knowing what we know now.

His difficulty handling the question provided an early warning sign that he might be a less skilled campaigner than many in the Republican establishment had assumed.

Then-President George W. Bush, right, bids farewell in 2006 to his brother, then-Florida Gov. Jeb Bush, who is now running for president in a 2016 field that is debating George W. Bush’s legacy. (Jason Reed/Reuters)

On Tuesday, Bush repeated his support for his brother’s decision to remove Saddam Hussein from office.

“I think the lesson’s learned are that we have to have a strategy to get in and a strategy to get out, which means that you create a stable situation,” he said.

Bush’s continued support of his brother has been received increasingly warmly among some nostalgic GOP hawks who argue that it was Obama’s decision to scale back involvement in Iraq that led to the rise of the Islamic State.

That argument received impassioned support from Sen. Lindsey O. Graham (S.C.) during Tuesday night’s undercard debate for trailing candidates.

“I’m tired of beating on Bush. I miss George W. Bush. I wish he were president right now. We wouldn’t be in this mess,” Graham said, his voice rising as some in the debate audience cheered.

The Obama administration’s 2011 military intervention in Libya in support of rebels seeking to topple longtime ruler Moammar Gaddafi has provided Republicans a way to criticize regime change without mentioning George W. Bush.

Hillary Clinton was a particularly strong voice for U.S. involvement, arguing as secretary of state that U.S. airpower should be used to assist rebels. In 2011, Gaddafi was killed in the midst of a Libyan uprising. The country is now split between rival governments, and the Islamic State has expanded its reach there.

During the debate, Paul argued that Libya proves that U.S. intervention has destabilized the region.

“When we toppled Gaddafi in Libya, I think that was a mistake. I think ISIS grew stronger, we had a failed state, and we were more at risk,” he said, using a common acronym for the Islamic State.

Sen. Ted Cruz (Tex.) noted that some Republicans backed Democratic-led intervention in Libya, which he said is now “a terrorist war zone run by jihadists.” He said lessons from Libya have not been heeded by Republicans now advocating that the United States arm rebels seeking to depose Syrian President Bashar al-Assad.

“We need to learn from history. These same leaders — Obama, Clinton and far too many Republicans — want to topple Assad. Assad is a bad man. Gaddafi was a bad man,” Cruz said. “[Former Egyptian leader Hosni] Mubarak had a terrible human rights record. But they were assisting us, at least Gaddafi and Mubarak, in fighting radical Islamic terrorists.”

Rubio, on the other hand, argued that Gaddafi had killed Americans and that a U.S. effort was needed to speed his removal and prevent even more chaos.

“The reason why I argued we needed to get involved is because he was going to go one way or the other,” Rubio said. “And my argument then was proven true, and that is the longer the civil war took, the more militias would be formed and the more unstable the country would be after the fact.”

Such questions have remained land mines for many candidates who do not want to advocate deep involvement in Middle Eastern countries but also believe the United States should support groups in Syria with the aim of stabilizing the country.

“There are moderates in Syria who we should be supporting,” said Ohio Gov. John Kasich. “I do not support a civil war. I don’t want to be policeman of the world. But we can’t back off of this.”