Palo Alto, Calif. — THE dramatic events of this past weekend mark a potential turning point in the modern history of the Middle East. Estranged for the last three and a half decades, the American and Iranian governments are talking and working with each other once again.

The implementation of the nuclear deal and the lifting of sanctions on Iran, as well as the prisoner exchange, combined to make it a rare, hopeful day for Washington and Tehran. But Iran remains a powerful adversary of America across nearly all the conflicts of the Middle East. President Obama and his successor in the White House will be tested by whether they can find the right balance between cooperation on nuclear issues and containment of Iranian aggression.

The deal will have multiple consequences. With the lifting of sanctions, Iran becomes a major player in global energy markets. It will also cease to be a political pariah in much of the world. Most important, a possible third major Middle East war has been averted and Iran’s bid for nuclear weapons stymied, at least for now. At a time of upheaval in the region, this is an unusual piece of positive news.

Despite criticism of the agreement from congressional opponents, there are clear benefits for American security. Iran’s nuclear program will be frozen for 10 to 15 years now that its plutonium production and uranium enrichment facilities have been largely dismantled. A vast majority of its enriched uranium has been shipped abroad. Tehran will be subject to tight international supervision and monitoring.