President Barack Obama gave up a day of sightseeing in India to meet the new king and crown princes of Saudi Arabia on Tuesday, an acknowledgement that the U.S. still highly values its 70-year-old relationship with the oil-rich monarchy.

But despite the show of friendship, tectonic plates are shifting in the region and the U.S. now has more options than relying on a country that -- despite modest reforms under the late King Abdullah and close security ties with Washington -- is still a prime source of the radical intolerance that inspires many anti-Western terrorist groups.

Over the past 18 months, the U.S. and Iran – Saudi Arabia’s rival -- have conducted a high-level bilateral dialogue that belies their 35-year lack of formal diplomatic relations. The near-daily negotiations that are going on now in Europe in an effort to reach a nuclear agreement are unprecedented in duration, depth and intimacy.

The two countries are also waging parallel fights in Iraq and to some extent, in Syria, against the group that calls itself the Islamic State (IS).

Even the advances of an Iran-backed group in Yemen, the Houthis, may not preclude cooperation against Al-Qaeda in the Arabian Peninsula, the terrorist organization that claimed responsibility for the horrific attacks on the Charlie Hebo magazine in Paris and that is, according to Undersecretary of Defense for Intelligence Michael Vickers, the “most dangerous” of al-Qaeda’s offshoots.

These shifts in the U.S.-Iran relationship make the rhetoric of some of those who criticize U.S. policy seem frozen in the past.

For example, one group of former U.S. officials wrote recently that the “United States and Iran are destined to remain adversaries” and that the U.S. should now be contemplating a “revamped coercive strategy” against Iran instead of redoubling efforts to reach an accord.

Sen. Ted Cruz (R-Tex.) went further, telling a conservative audience on Sunday that the multilateral nuclear talks – which have already paused Iran’s nuclear advances -- were “the worst negotiation in the history of mankind.”

Cruz predicted that Iran would soon be capable of attacking “Tel Aviv, New York or Los Angeles” with nuclear weapons – implausible given the slow progress of Iran’s missile program,  close international scrutiny of its nuclear facilities and the fact that any such strike would be suicidal.

Cruz, who is considering a run for the Republican presidential nomination, sidestepped this logic by labeling Iran’s ruling Shi’ite clerics “radical Islamic nutcases.”

Fortunately, the Barack Obama administration has its own analysis and is thinking much more strategically.

As the 19th century British statesman, Lord Palmerston, once said, “Nations have no permanent friends or allies, they only have permanent interests.”

Permanent interests led former U.S. President Richard Nixon to go to China and initiate détente with the old Soviet Union to increase U.S. options during the Vietnam war. U.S. interests have brought Washington to the negotiating table with Iran to stave off the spread of nuclear weapons and find new approaches to the chronic crises of the Middle East. 

Opponents of a deal have no reasonable alternative to negotiations. In the current environment in the Middle East, the U.S. is not going to bomb Iran’s nuclear facilities, put U.S. boots on the ground in Syria or send combat forces back to Iraq.

Contrary to the fear-mongers, Iran is not “on the march” in the region and is stretched rather thin propping up what is left of the regime of President Bashar al-Assad in Syria, assisting the Iraqi government of Haider al-Abadi and supporting Hezbollah in Lebanon.

Far from being “radical Islamic nutcases,” Iran’s leaders are realists who want to restore stability to their neighborhood but are opportunistic enough to take advantage of others’ missteps, such as the U.S. invasion of Iraq. Not surprisingly, Iran wants its neighbors to take its interests into account.

Iran also has internal politics to consider. Hardline elements nit-pick the nuclear negotiations and pounce on symbolic if trivial matters, such as Iranian Foreign Minister Javad Zarif’s recent stroll in Geneva with U.S. Secretary of State John Kerry.

The hardliners know how popular a nuclear agreement would be among the general public and are worried that a major success for the administration of Iranian President Hassan Rouhani would cause them to lose their grip on Iran’s parliament in elections scheduled next year.

Elections are also on the mind of Israeli Prime Minister Benjamin Netanyahu who appears willing to further jeopardize relations with the Obama administration by accepting House Speaker John Boehner’s invitation to address a joint session of the U.S. Congress on March 3, two weeks before Israelis are to vote.

The invitation – which blindsided the White House and the State Department – may help shore up Netanyahu’s right-wing base but appears to have backfired if the Israeli leader’s intention was to encourage Congress to vote soon on new sanctions against Iran.

Democratic Party support for more sanctions appears to be eroding and a vote on the Senate floor on any of several sanctions bills seems increasingly unlikely before the end of March.

Most Democrats appear to have accepted President Obama’s argument that voting even on “sanctions in waiting” would jeopardize the complicated nuclear talks.

As for the Saudis, fears of a succession crisis turned out to be overblown, as the Kingdom put in place a new monarch, crown prince and deputy crown prince – the latter from the generation of the founder’s grandsons – before Abdullah’s body had even grown cold.

Still, all the U.S. reassurance in the world cannot compensate for Saudi shortcomings.

Wahhabi Islam remains the source of the practices espoused by IS and other jihadi groups. Despite some reforms under Abdullah, including increasing educational opportunities for young Saudis,  women remain second-class citizens, freedom of expression is heavily restricted and anti-government criticism that would be tame in the West is a flogging offense.

Iran, too, abuses human rights but its society is less constricted and its people are generally welcoming to Americans.

Most Iranians are eager for end to their pariah status, which they hope would result from a nuclear deal. Rather than seeking to jeopardize a breakthrough, critics – in the U.S. and abroad -- should give the diplomatic process all the breathing room it needs.

By Barbara Slavin : She is a senior fellow at the Atlantic Council’s South Asia Center and a correspondent for Al-Monitor.com, a website specializing in the Middle East. She is the author of a 2007 book, Bitter Friends, Bosom Enemies: Iran, the US and the Twisted Path to Confrontation, and is a regular commentator on U.S. foreign policy and Iran on NPR, PBS, C-SPAN and the Voice of America.