WHAT SEEMS lost in the furious, partisan debate about the Iran nuclear deal is just how long it took the United States to actually get back to a negotiating table with the Iranian government — nearly 35 years.

The talks have already achieved something tangible and rare: The United States and Iran are talking again, after decades of a bitter divorce and near total isolation from each other.

While neither really wants to admit it, Democrats and Republicans worked in tandem to get us to this point. Most Democrats don’t give President George W. Bush enough credit for his critical decision in 2005 to seek negotiations with Iran before considering the use of force.

Similarly, most Republicans can’t bring themselves to admit that President Obama has been skillful in adopting Bush’s original construct of combining tough sanctions and the threat of force with diplomacy to pressure Iran to negotiate.

Because we had been isolated from Iran for so many decades, both presidents also suffered from the diplomatic handicap that we simply did not know enough about what makes Iran tick.

The deep freeze between the two countries began when Iran’s revolutionary government held 52 American diplomats hostage for 444 days in 1979-81. The United States rightly broke diplomatic relations, and embassies in both Washington and Tehran were closed.

The result was that from 1980 on, hardly anyone in my generation of American Foreign Service officers traveled to Iran, interacted meaningfully with Iranian diplomats, or studied Farsi. We lost our collective knowledge of one of the foundational civilizations in the Middle East.

When Secretary of State Condoleezza Rice asked me to organize a new Iran effort at the State Department in 2005, I went looking for expertise in our respected Near East bureau. To our surprise, we discovered the extent of our ability to follow events in Iran was exactly one officer who spent half his time on Iran. That was it. To her credit, Rice ordered the creation of a much larger Iran desk. We encouraged younger officers to become Iran experts and to learn the language and culture. Rice wanted us to have a smarter and more sophisticated understanding of Iranian politics, economics, and society because, as she wrote, “we were making policy on Iran with one hand tied behind our back.”

Bush and Rice also overturned their prior skepticism about talks and joined with the Europeans, Russia, and China to offer negotiations on the nuclear issue to Iran in 2006 and again in 2007. But Iran refused. That is when we turned to sanctions, passing three Chapter VII resolutions against them at the United Nations. We also introduced US financial sanctions. Obama then strengthened those sanctions in his first term in office.

This history is important because it reminds us that it took a highly integrated campaign by Democratic and Republican administrations, along with our partners, to force Iran to accept negotiations. In foreign policy, one president hands the baton of leadership to his or her successor. In this case, the Bush and Obama policies reinforced each other. We will need this bipartisan unity in dealing with a difficult and often mendacious Iranian government for a decade or more to come on the nuclear issue.

Diplomacy may or may not turn out to be the vehicle that resolves our differences with Iran. But there is at least the possibility that diplomacy’s redemptive powers might open new opportunities with this once implacable adversary.

Congress is moving this week to insert itself into the negotiations with Iran. Senior Republicans and skeptical Democrats would be wise to do so in a way that strengthens rather than weakens the president’s hand in the difficult negotiations with Iran this spring.

The president and his team know the road to a final agreement by June 30 will be long and problematic. They know substantial differences persist. They also understand that Iran needs a final deal more than we do. But let’s not give up on Obama’s diplomacy. It is still the surest path to where we should want to be with Iran after the deep freeze of the last three decades — working out our differences at a negotiating table rather than on a distant battlefield.