For US President Barack Obama, the interim deal to cap Iran's nuclear program is a belated down payment on the transformative foreign policy he always envisioned.
That is one reason why his Republican foes are suspicious of the pact, viewing it as typical of a diplomatic doctrine rooted in weakness and an over eagerness to engage America's enemies at the expense of its friends.
The deal, forged after intense negotiations between Tehran and world powers, is the most serious breakthrough in more than 30 years of near hatred between Washington and Iran.
It means more to the president than a rare win in a grim political season: it represents hopes of validation for several core aspects of his political vision -- including the idea that America should talk to its enemies; that military force should be a true last resort; and that non proliferation should be at the center of US foreign policy.
If the Iran initiative evolves into understandings wider than the nuclear issue, it would offers an opening for Obama to transform his legacy as a statesman.
It also comes as the prime rationale of his domestic agenda -- the idea that an activist government is a force for good -- is being tested by the woeful debut of his health care law.
The Iran deal gestated far from the high-stakes talks at a plush hotel in Geneva. It was first hinted at during a 2007 Democratic presidential debate in South Carolina.
At that event Obama repudiated the Bush administration's 'axis of evil' talk, and shocked the foreign policy establishment by offering to engage US enemies, including Iran.
"The notion that somehow not talking to countries is punishment to them . . . is ridiculous," Obama said, invoking US-Soviet talks led by presidents John F. Kennedy and Ronald Reagan.
Obama, in his first inaugural address, offered a hand to US foes if they would "unclench" their fists, but failed to coax Iran into dialogue during his first term.
Until the election of the 'moderate' President Hassan Rouhani, this year, engaging the enemy bore little fruit, with the possible exception of the US-engineered opening of military-ruled Myanmar.
Obama aides argue that his foreign policy's successes include bringing US troops home from Iraq, and from Afghanistan by the end of 2014.
But his legacy lacks the highlight that detente with Iran would enshrine, an accomplishment comparable to major presidential wins like Richard Nixon's 'opening' of China, or Ronald Reagan's ending of the Cold War.
Obama, who rose to power railing against a "dumb war" in Iraq, has made it an article of faith to avoid Middle East conflicts of unknowable consequences.
He was mocked for "leading from behind" in Libya, and for his 11th hour blink on striking Syria. He prefers the fearsome but arms length US drone war.
Any deal to end Iran's nuclear program, however imperfect, that avoids the US military action he insists he reserves the right to wage, would gel with his worldview.
"Military options are always messy," Obama said when asked about Iran last week.
"They're always difficult, always have unintended consequences, and in this situation are never complete in terms of making us certain that they don't then go out and pursue even more vigorously nuclear weapons in the future."
Political wags sometimes quip that Obama is finally earning the Nobel Peace Prize he was prematurely awarded in 2009. The punchline might be punctured if he conceives a long-term nuclear settlement with Iran.
But Obama's domestic foes are not convinced.
Many balk at the idea of talking with a nation that has flayed the United States for decades as an "evil empire."
Obama's diminished standing a year into his second term hardly helps.
"This administration is . . . very long on announcements but very short on follow through," Bob Corker, the top Republican on the Senate Foreign Relations Committee, told Fox News Sunday.
For Mike Rogers, Republican chairman of the House Intelligence committee, Iran has received "a permission slip to continue enrichment -- that's the one thing the whole world was trying to stop them from doing," he told CNN.
Despite the antipathy on Capitol Hill, Obama can use executive power to fulfill the US part of offering a "modest" $7 billion in sanctions relief in return for Iran taking steps to halt progress in its nuclear program.
After administration lobbying, new sanctions to be debated in Congress in December will be timed to come into force in six months at the end of the interim deal, and if no final agreement is reached.
But Congress would have to lift sanctions under any final deal, and Obama faces a tough slog to convince lawmakers suspicious not only of Iran -- but of their own president.