WASHINGTON (AP) -- President Barack Obama vigorously defended the nuclear deal with Iran on Wednesday, casting the historic accord as the only possibility to avert a war with Iran and a nuclear arms race in the Middle East.

President Barack Obama answers questions about the Iran nuclear deal during a news conference in the East Room of the White House (AP Photo/Pablo Martinez Monsivais)

With his foreign policy legacy on the line, Obama put the onus on the deal's critics to voice an alternative, and said those who prefer a military strike should own up. He said the U.S. faces a "fundamental choice" - aiming his comments squarely at Congress, where lawmakers face a two-month window to try to thwart the deal.

"If we don't choose wisely, I believe future generations will judge us harshly," Obama said, describing a potentially squandered opportunity to make the Mideast and the world a safer place.

Yet in a reminder of the tough road ahead, Obama conceded that the deal will do little to quiet many other U.S. concerns about Iran. He acknowledged it was likely that the easing of economic sanctions would free up funds that Iran could use to sponsor terrorism against Israel or other countries.

"That is a likelihood," Obama said, though he predicted it wouldn't be a "game-changer."

As Obama spoke at the White House, the deal's critics - including Israeli Prime Minister Benjamin Netanyahu - were only growing more outspoken. Addressing his country's parliament on Wednesday, Netanyahu said Israel was not bound by the agreement, suggesting Israel could still take military action against Iran's nuclear program even if the deal proceeds.

"We will reserve our right to defend ourselves against all of our enemies," Netanyahu said. "We have strength, and it is great and mighty."

Under the deal announced Tuesday, Iran's nuclear program will be scaled back and closely monitored as the U.S. and world powers seek to cut off Iran's ability to develop a nuclear weapon. In exchange, Iran will see biting economic sanctions eventually lifted, freeing up billions of dollars in oil revenue and frozen assets.

In the absence of a deal, Obama said, the international economic sanctions that brought Iran to the negotiating table will unravel, and the world community will be unable to put the sanctions regime back together.

"Without a deal, we risk even more war in the Middle East, and other countries in the Middle East would feel compelled to develop their own nuclear weapons," Obama said, adding that such a chain of events would risk a nuclear arms race "in the most dangerous region in the world."

As Obama defended the deal, his allies were mounting a concerted push to sell the agreement to skeptics, while its critics warned of dire consequences.

Vice President Joe Biden spent the morning on Capitol Hill briefing House Democrats, and told reporters he was confident that lawmakers would get behind the deal. Yet in Jerusalem, Israeli leaders were planning what is expected to be a lobbying effort in the U.S. Congress ahead of a review of the deal, starting with a visit to the U.S. by Netanyahu's political rival, Isaac Herzog.

In Tehran, Iranians took to the streets to celebrate the accord, and even Iran's hard-liners offered only mild criticism - a far cry from the outspoken opposition that the White House had feared. At the United Nations, the U.S. began circulating a draft Security Council resolution to authorize the deal.

Opponents of the deal, including Israel, have lambasted the Obama administration for granting sanctions relief to Iran while it continues to fund terrorist groups in places like Syria, Yemen and Lebanon. Obama said the U.S. would keep trying to gain Tehran's cooperation on other security issues, but acknowledged the Islamic republic might not change its behavior.

"We're not betting on it," he said.

Aiming to frame the parameters for the growing debate, Obama bemoaned that his political opponents have wielded "speculation or misinformation" about the deal. While he said he hoped Congress would approve the deal based on the facts, he conceded that "we live in Washington, and politics do intrude."

"I am not betting on the Republican Party rallying behind this agreement," Obama said.

Obama sought to rebut specific critiques that have been lobbed at the deal - such as concerns about whether sanctions can really be "snapped back" into place if Iran cheats. Obama insisted that they could, even if Russia or China objects.

He rejected concerns that Iran could use procedural delays to stop inspectors from examining suspicious military sites until it was too late by arguing the world would have a full year to intervene before Iran could feasibly put together a bomb.

Although a longstanding embargo on selling arms to Iran will sunset in five years, Obama shrugged off that concern, too. He said the U.S. and its partners have other ways to prevent Iran from sending weapons abroad.

The historic engagement with Iran - a U.S foe since the 1979 Iranian Revolution - has sparked speculation some diplomatic circles that it could lead to a broader detente between the two countries. In Iraq, American and Iranian forces that are both fighting Islamic State militants have sought to stay out of each other's way, but Obama insisted there would be no formal cooperation with Iran on the IS threat despite the nuclear deal.

Across the U.S. and in many Western nations, television networks carried Obama's remarks on live TV. But Iranians hoping to tune in found fewer opportunities. Iranian state TV did not show Obama's speech in real time, despite carrying his formal announcement live only a day earlier.

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