With a potentially historic agreement on Iran’s nuclear program in place, President Obama immediately focused his attention on the fight at home. When he announced the deal Tuesday morning, the president warned Congress that he would “veto any legislation that prevents the successful implementation of this deal.” A few hours later, he sat down with the New York Times’s Thomas Friedman to sell it on its merits.

“We are not measuring this deal by whether it is changing the regime inside of Iran,” the president said. “We’re not measuring this deal by whether we are solving every problem that can be traced back to Iran, whether we are eliminating all their nefarious activities around the globe.”

The aim of the negotiations was on ensuring that “Iran could not get a nuclear weapon.”

And that is where he wants the ensuing debate over the final terms of the agreement to be focused. “What I’m going to be able to say, and I think we will be able to prove,” he told Friedman, “is that this by a wide margin is the most definitive path by which Iran will not get a nuclear weapon, and we will be able to achieve that with the full cooperation of the world community and without having to engage in another war in the Middle East.”

That is what the president would like people to believe. But it may not be so simple.

Congress has 60 days to review the deal for final approval, but many GOP leaders have declared the agreement dead on arrival. Some Republicans, as I noted, lambasted the administration for appeasing the Iranian regime even before the details were announced. Accordingly, the administration will likely focus most of its time on reassuring skeptical Democrats to block the passage of legislation that would undo the deal, or, failing that, to sustain a veto.

An override seems unlikely, but the coming congressional debate will not be limited to the merits of the deal.

As Justin Logan and John Glaser wrote on CNN.com:

The debate over Iran diplomacy was really two debates, in which each side was arguing over something different. On the one side was a strikingly broad consensus of nearly the entire arms control community, which recognizes what the deal can achieve in terms of nonproliferation and regional stability. On the opposing side is the Iran hawk community, which focused less on the nuclear issue than on finding ways to isolate and ultimately destroy Iran’s clerical regime, by military force if necessary, nuclear program or not.

The agreement is a clear success for nonproliferation advocates. Unfortunately, that’s not what matters to some of those who now control its fate.