President Richard Nixon listens as details of the Great Wall of China are explained near Peking on Feb. 24, 1972. To his right are first lady Pat Nixon and Secretary of State William P. Rogers. (AP)

In accepting the Nobel Peace Prize in 2009, President Obama defended his overture to Iran and other foes by citing President Richard Nixon’s opening to China in 1972.

“In light of the Cultural Revolution’s horrors, Nixon’s meeting with Mao appeared inexcusable — and yet it surely helped set China on a path where millions of its citizens have been lifted from poverty and connected to open societies,” Obama said.

“No repressive regime can move down a new path unless it has the choice of an open door,” he said.

With less than three weeks left to negotiate a framework for limiting Iran’s nuclear program, Obama hopes that Iran’s leaders, like the Chinese Communist Party leader Mao Zedong, will put aside mistrust and step through “an open door” that could alter the geo­politics across the region.

But Obama is not Nixon, and Iran is not China, and the comparison — made in newspaper columns and by some foreign policy experts — is illuminating largely because of important differences it exposes.

Nixon’s visit to China was a powerful symbol — a longtime anti-Communist president strolling along the Great Wall and dining with senior party leaders. Unlike Nixon, Obama lacked a political record that would shield him from criticism for reaching out to a longtime foe.

China also welcomed Nixon’s visit, whereas Iranian leaders still harbor suspicion of the United States. The detailed nuclear accord with Iran, if it can be cemented, could lower tensions over nuclear weapons, but no one expects a presidential visit to either country; the cultural, political and strategic gaps are likely to remain wide.

“This opens the door in a different way from the way the China door was opened to follow-on activities,” said Thomas R. Pickering, a five-time U.S. ambassador. “Nobody is talking about establishing diplomatic relations.”

From the start of his presidency, reaching out to Iran has been more difficult for Obama than reaching out to China had been for Nixon. In early February 2009, the U.S. women’s badminton team was invited to take part in an international tournament in Tehran, an echo of the ping-pong team that visited China in one of the first signs of a thaw.

But the possibility of shuttlecock diplomacy fell apart when the Iranian Foreign Ministry said there wasn’t enough time to approve the visas.

The business community has provided little support. While U.S. corporations had long pined for access to the Chinese market of then nearly 1 billion people, Iran has a population of just 80 million people and the economy is already developed. An opening with Iran would mostly interest a handful of big oil companies.

Iran also continues to hold in prison Washington Post correspondent Jason Rezaian; in 1971, there were no U.S. correspondents based in China.

Like China and the United States in the early 1970s, strategic issues have driven Tehran and Washington into direct contact, first under President George W. Bush and then Obama. Iranian nuclear weapons would pose a dire threat to Israel and other countries in the region, and Iran has supported Hezbollah in Lebanon, President Bashar al-Assad in Syria, the Iraqi government, Hamas in Gaza and Shiite factions in Yemen. Yet Iran wants to ease broad economic sanctions.

In 2009, Obama had said “that sanctions without outreach — condemnation without discussion — can carry forward only a crippling status quo.”

Talks over Iran’s nuclear program intensified in the fall of 2013 when a new Iranian negotiating team led by Foreign Minister Mohammad Javad Zarif reached a Joint Plan of Action with the permanent members of the U.N. Security Council plus Germany. As a self-imposed deadline approaches, some details have leaked; the deal is described as covering more than 10 years and limiting, but not eliminating, centrifuges that are needed to make bomb-ready enriched uranium.

Nixon relied on secret advance talks between national security adviser Henry A. Kissinger and Chinese Premier Zhou Enlai. In those meetings, the two sides hammered out everything from terms over the status of Taiwan to the wording of the Chinese invitation to Nixon.

In the public glare, Taiwan could have been a stumbling block. China claimed the self-governing island as its own territory, and the United States had long treated Taiwan as the legitimate government. Nixon finessed the issue, without having to worry about a revolt in Congress like this week’s letter to Iran signed by 47 Republican senators.

Publicity “would have mortgaged our prospects with Beijing,” Kissinger wrote later. “Transparency is an essential objective, but historic opportunities for building a more peaceful international order have imperatives as well.”

Both Nixon and Mao had strategic reasons for easing tensions. China and the Soviet Union were occasionally exchanging fire over disputed borders. Mao wanted to “change ­horses,” Pickering said. Nixon was looking for a counter­weight to the Soviet Union.

Some foreign policy experts think that the current threat from the Islamic State could provide a unifying push, like the Soviet threat once did. Worried about that prospect, Israeli Prime Minister Benjamin Netanyahu warned in his speech to Congress this month that “when it comes to Iran and ISIS, the enemy of your enemy is your enemy.”

Some experts still see the Nixon-China opening as a template for transforming relations with Iran and the entire Middle East.

In the 2013 book “Going to Tehran,” former National Security Council staff members Flynt Leverett and Hillary Mann Leverett argued that Obama should do something that “parallels the Nixon-Kissinger opening to China.”

“To me it’s a critically important model,” Hillary Leverett said in an interview. “The nuclear agreement, as flawed as some see it, could be negotiated so it could be used as a sort of Shanghai communique, allowing us to realign relations in the Middle East, not to renounce alliances­ but to rebalance and to allow Iran to come into the mix of relationships.”

But James Mann, author of “About Face” on U.S.-China relations and a fellow at the Johns Hopkins School of Advanced International Studies, warns that emulating Nixon’s visit to China isn’t so easy.

“People have tried to duplicate Nixon in China over and over again, including Iran,” Mann said. He cites the ill-fated 1986 journey by President Ronald Reagan’s national security adviser Robert “Bud” McFarlane, who traveled to Tehran carrying a Bible with a handwritten verse from Reagan and a key-shaped cake as a goodwill gesture for Iranian leaders.

“One way or another people have been trying to pull off that diplomatic triumph, which would be a huge surprise and would end a long estrangement,” Mann said.

Mann says that the talks with Iran have focused on Tehran’s nuclear program whereas Nixon and Kissinger had a long list of unwritten strategic understandings that emerged from discussions with Zhou and Mao. The United States said it would keep Japan from obtaining nuclear weapons and restrain China’s Asian rivals. Zhou indicated that China would not intervene to make the U.S. withdrawal from Vietnam any harder than it was.

Zhou also touched on the Cultural Revolution still in progress in China. Why? “Because the objective was to go beyond normalization to what our interlocutors called friendship, but which would be more accurately described as strategic cooperation,” Kissinger wrote.

Yet Mann notes that Nixon failed to get one of his top priorities: Chinese help in ending the Vietnam War. And embassies did not open for several years.

Hillary Leverett, who negotiated with Iran over al-Qaeda and Afghanistan during the Bush administration, thinks that Secretary of State John F. Kerry and his Iranian counterpart, Zarif — whom she calls the Kissinger of our time — must be touching on non­nuclear strategic issues just as Kissinger and Zhou did.

“Kerry has been spending a lot of time with Zarif,” she said. “I’d be shocked if they had spent all these hours over the number of centrifuges.”

That’s what worries Republicans in Congress, many of whom pressed Kerry in a hearing Wednesday.

“There is no grand bargain being discussed here in the context of this negotiation,” Kerry said in reply. “This is about a nuclear weapon potential. That’s it.”