In "Practicing History," historian Barbara Tuchman observed that there are "two ways of applying past experience: One is to enable us to avoid past mistakes and to manage better in similar circumstances next time; the other is to enable us to anticipate a future course of events."

Tuchman would find it strange today that many of the loudest opponents of the Iran nuclear agreement are the same prominent individuals and organizations who unequivocally supported the most significant national security blunder by the U.S. in recent memory, the war of choice in Iraq.

As evidence has accumulated since the failure to find weapons of mass destruction in Iraq, the price of that foreign policy engagement has become obvious to most. The cost to the U.S. includes trillions of dollars lost to future generations of Americans, tens of thousands killed or injured, the opening of a Sunni-Shia Pandora's box of sectarian strife, the ascendance of Iran and the diminished influence of the U.S. in the Middle East.

Remarkably, there are still unrepentant cheerleaders for that war, as well as those who argue that the U.S. invasion was a good idea in principle that was just executed poorly. And they are among the most influential voices opposed to the agreement with Iran.

Why does it matter that the pundits who were so convinced about invading Iraq more than a decade ago now pursue with passionate certainty the defeat of the diplomatic effort involving Iran?

It matters because, then and now, these voices suffer from a greatly exaggerated view of the ability of the U.S. to unilaterally dictate geopolitical outcomes that we desire. In the case of Iraq, this was perhaps best expressed by former Vice President Dick Cheney who, when pressed before the war on our capacity to remake Iraqi society, argued that we would be "greeted as liberators." Of course, the experience in Iraq, the resulting ascendance of Iran and reduced U.S. influence in the region have only further diminished our capacity to act without the support of others and have underscored the importance of smart power — diplomacy backed with all of the resources at our disposal to achieve our objectives.

The nuclear agreement, now endorsed unanimously by the United Nations Security Council, is long and complex, and it is presumed that Congress will study carefully the details. Are the verification provisions adequate and does the International Atomic Energy Agency have the resources to monitor compliance? What is the process by which sanctions could be reimposed if violations occur? Are all paths to a nuclear bomb blocked? What are the alternatives to this approach and are they acceptable to the American people?

Our expectation is that a serious examination of this agreement should win over a bipartisan majority. The agreement's substantial reductions in uranium stockpiles and installed centrifuges, robust inspection regime and dramatically diminished capacity for an Iranian breakout and "race to a bomb" provide unprecedented means to ensure Iran will meet its stated commitment to never build a nuclear weapon.

But these elements will not win over those with an unrealistic view of the capacity of the U.S. to play the Lone Ranger in international politics. And while opponents say they support diplomacy, the so-called alternatives they would prefer — like pressing for a harder line on sanctions relief — would put us at odds with our allies, be rejected by Iran and increase the risks of another war in the Middle East that would be tragic for both the U.S. and for Israel.

The nuclear agreement will of course pose challenges for U.S. policymakers, as sanctions relief will provide benefits to Iran and opportunities to make mischief in the region. But through our continued presence, support of regional friends and allies, and an enforceable nuclear agreement, we have the strongest capacity to manage such challenges effectively.

Americans must hope that Congress will be preoccupied with the substance of the Iran agreement and the poor alternatives to it, and not be influenced by voices of the past that cling to dangerous views about our prospects as a go-it-alone superpower. Congress should "practice history" and recognize that this agreement has the potential to interrupt the downward spiral in the region, from conventional war and terrorism to nuclear conflict.

Forcing the president to veto a rejection resolution would reflect badly on the Congress and the United States of America. Even worse, overriding a presidential veto would have grave implications for the U.S., for Israel and for the region for many years to come.

Brian Atwood is senior fellow at Brown University, formerly dean of the Humphrey School of Public Affairs at the University of Minnesota and U.S. assistant secretary of state for congressional relations. Eric Schwartz is dean of the Humphrey School and formerly assistant secretary of state for population, refugees and migration and special assistant to the president for national security affairs.