The undercurrent of the whole news conference Wednesday afternoon, and of President Obama's overall defense of the Iran deal, is the argument that American power is limited — that this is the best deal we could get with our declining leverage. His defenders call it realism; it also may amount to ratifying retreat.

There's little that Obama's Republican critics in Congress can do about the deal other than vote their symbolic disapproval, and the president seemed to be speaking as much for the history books as for contemporary critics, using phrases such as "historic chance" and "future generations." But mostly what came through was a defense of what future historians may describe as the Obama doctrine: an America that recognizes the limits of its power and acts less ambitiously.

This is why it was, sadly, a powerful case — for American weakness.

DANA MILBANK, Washington Post

At the very least, the deal is significant in that it will slow the pace of Iran's nuclear development. But will Tehran really adhere to this agreement? There is no reason to be optimistic.

THE JAPAN NEWS/YOMIURI

The U.S. has a long history of presidents, including Republican ones, striving to address nuclear dangers through negotiation instead of war. Every president going back to Dwight Eisenhower has pursued — and in most cases achieved — agreements involving doomsday weapons.

But the U.S. also has a long history of critics treating such efforts as products of blindness, wishful thinking and cowardice. Obama can take some consolation in knowing that Richard Nixon and Ronald Reagan were also vilified as craven dupes. George W. Bush's efforts in the North Korea talks were labeled "immediate surrender."

Welcome to the club.

History indicates that even conservatives, when they reach the Oval Office, come to appreciate the value of negotiating on nuclear disputes rather than going to war. The critics? They never learn.

STEVE CHAPMAN, Chicago Tribune

The deal makes further conflict in the region certain even apart from its nuclear provisions. We are, in essence, arming our enemy and bolstering its economy so it can continue to attack our allies in the region. Aside from the moral monstrosity of the proposition, we invite further attacks on Sunni states and Israel, and, at some point, a military showdown with an emboldened Iran.

If lawmakers are worried about the prospects for war in the region and U.S. credibility, there is no real choice but to reject this deal.

JENNIFER RUBIN, Washington Post

Normalizing relations between one of the largest military powers in the Middle East and the major powers of the West is a huge, game-changing event. What is perhaps most fascinating about this deal is the role and ambitions of China and Russia.

China's motives are more obvious: It would like to blunt the projection of U.S. military power around the world, and — most of all — reduce geopolitical tensions that tend to raise oil prices.

Russia's interests are more complex, since it benefits from higher oil prices. Putting Iran's huge oil production back on the market could exacerbate today's global crude glut. So what's driving the Russians to be so cooperative?

Russian President Vladimir Putin is smartly playing a long game. Lower oil prices will be painful in the short run for Russia. But an aggressive U.S., with an expansionist military around the world, may be even worse. Hence, the surprising willingness of Russia to sign on to an agreement to lift sanctions against Iran.

Watch the price of oil. Consider what increases in supply and reduction of Middle East tensions do to its price. Then imagine what that could mean for the global economic recovery.

Barry Ritholtz, Bloomberg View

Critics of this agreement fear that, at best, it will keep Iran from getting a nuclear weapon for "only" 10 years. The administration says the timeline is longer, but what if it's 10 years? Walking away from the table wouldn't buy us more time.

E.J. DIONNE, Washington Post

Administration officials must do a lot of explaining about how Iran can be kept on the straight and narrow. But — even assuming they make a convincing case — Obama also must spell out how he intends to prevent a sanctions-free Tehran from further destabilizing the Middle East.

The president must explain why he caved in accepting a provision to lift an arms embargo on Iran in five years and an embargo on sales of ballistic missiles in eight years. He must also explain how he means to convince Iran that he isn't its patsy.

Unless Obama can take off his blinders, this deal will encourage Iran to become even more aggressive in the region. It may also encourage Sunni Arab states to develop nuclear programs in an effort to match Iran.

Obama can't make a convincing case for an Iran deal until he brings his Mideast policy in line with facts on the ground.

TRUDY RUBIN, Philadelphia Inquirer

Yes, a richer Iran will have more money to spare for military aggression in the region. And those who think the regime will suddenly become more peaceful and cooperative are deluding themselves. (Did financial success make Putin less aggressive?) But it isn't feasible to maintain the nuclear sanctions indefinitely.

The negotiators have just bought some time. Israeli Prime Minister Benjamin Netanyahu called Tuesday's agreement a "historic mistake," the same phrase he used to describe the temporary agreement struck in November 2013. He was wrong about that one: It froze or reversed Iran's nuclear progress for more than 18 months. This deal promises to deepen those gains and extend them for 10 years. When that time has passed, maybe U.S. and Israeli airstrikes will have to follow — or maybe not. But why rush to war now?

MARC CHAMPION, Bloomberg View

When you listen to the critics, ask yourself: Are they offering any kind of plausible alternative?

Without this pact, we're left with what? More economic sanctions that hurt the civilian population as much as Iran's leaders? A military strike that may or may not completely wipe out Iran's nuclear capability, but that could spark a wider war in the Middle East, where there is more than enough bloodshed already?

Yes, this agreement should be closely vetted. But until opponents come up with a realistic strategy, it is the best option available.

SACRAMENTO BEE

We have seen what comes of U.S. involvement in Middle East wars — destabilization, new terrorist threats and more war.

The pact with Iran announced Tuesday is about diminishing the chances of the United States going to war to stop Iran from deploying a nuclear weapon. To that end, the U.S. and its negotiating partners forged a sound deal. Obama and Secretary of State John Kerry should be hailed for a historic achievement.

KANSAS CITY STAR

Opponents need to explain what happens if the rest of the world accepts this deal, Iran says it is ready to implement it — and Congress blocks it. Will the European Union, which explicitly commits in the agreement to lift sanctions once Iran has fulfilled its main nuclear responsibilities, not do so because Congress says no? Can sanctions really be sustained in these circumstances, particularly if the Iranians don't increase their enrichment and say they will observe the deal? Could we be faced with a world in which the sanctions regime collapses, Iran gets its windfall and is only two months from breakout, and there is little on-ground visibility into its program?

Maybe the answer is no, but the skeptics need to explain what we can do to ensure that.

DENNIS ROSS, Washington Post

The final deal with Iran does what no amount of political posturing and vague threats of military action had managed to do before. It puts strong, verifiable limits on Iran's ability to develop a nuclear weapon for at least the next 10 to 15 years and is potentially one of the most consequential accords in recent diplomatic history, with the ability not just to keep Iran from obtaining a nuclear weapon but also to reshape Middle East politics.

That said, no one should have any illusions about Iran. Once sanctions are lifted, it stands to gain access to billions of dollars from accounts in international banks that have been frozen and from new oil exports and other business deals. The U.S. has to be extremely vigilant in monitoring how Iran uses those new funds and in enforcing those sanctions. [But] it would be irresponsible to squander this chance to rein in Iran's nuclear program.

NEW YORK TIMES

If the transformation of Iranian behavior the president hopes for does not occur, the deal on its nuclear program may ultimately prove to be a poor one — a temporary curb that, when it lapses, will enable a dangerous threshold nuclear state that poses a major threat to the U.S. and its allies.

Obama sketched a dark picture of the alternative to the agreement, in which the world would refuse to join in sanctions, Iran would step up its nuclear activities and the risk of war would grow. Whether the administration could have held out for a better bargain is certainly debatable; Obama settled for terms far short of those he originally aimed for. But with the deal now done, its rejection by Congress would likely create the unfavorable scenario the president describes. Whether he is right in claiming that his successor in 10 or 15 years "will be in a far stronger position" with Iran will depend on whether his hopeful theory about its political future proves correct.

WASHINGTON POST

To sell this deal to a skeptical Congress, Obama clearly has to keep his argument tight. But I suspect his legacy on this issue will ultimately be determined by whether the deal does, in the long run, help transform Iran, defuse the U.S.-Iran cold war and curtail the spread of nuclear weapons in the Middle East — not foster their proliferation.

That, though, will be a long time in determining. For the near term, the deal's merit will be judged on whether Iran implements the rollback of its nuclear enrichment capabilities to which it has agreed and whether the deeply intrusive international inspection system it has accepted can detect — and thereby deter — any cheating.

THOMAS L. FRIEDMAN, New York Times

Maybe the real benefit, at least from Obama's perspective, is that the nuclear deal will pave the way for America's full exit from the Middle East. After more than a decade of war and nation-building, the region is less stable and more dangerous than it was on 9/11. The Atlantic's Peter Beinart, who supports the deal, says what its critics are really doing is "blaming Obama for the fact that the United States is not omnipotent."

Perhaps we have reached the limits of what American leadership can do in that part of the world. But if that's true, Obama should have the decency to level with us about it. This deal is not an affirmation of American leadership. It's a recognition of American exhaustion.

ELI LAKE, Bloomberg View

There are skeptics in both parties, and many of their concerns are legitimate. But Obama and his aides are relying on a three-word question to protect the agreement from congressional interference: "Compared to what?"

"That's the killer argument," one of the U.S. participants in the negotiations told me.

They're right. Anyone who proposes rejecting this nuclear deal should be required to lay out an alternative course, and to show clearly that the alternative is both feasible and better.

The deal's opponents haven't really done that — because there are no easy alternatives.

DOYLE MCMANUS, Los Angeles Times