Not many high-profile Republicans have anything nice to say about the Iran deal.

But former Treasury secretary Hank Paulson – the guy who was in charge of the government’s sanctions operation under President George W. Bush, when the international community was just setting up this regime of punitive measures over Iran’s nuclear ambitions – thinks at this point, it would be pretty ill-advised to back away.

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“It’s somewhere in between naive and unrealistic to assume that after we’ve, the United States of America, has negotiated something like this with the five other, you know, parties and with the whole world community watching, that we could back away from that – and that the others would go with us, or even that our allies would go with us,” Paulson said during a forum sponsored by the Aspen Institute on Thursday night to discuss his new book on China.

“And unilateral sanctions don’t work, okay?” Paulson continued. “They really have to be multilateral.”

Paulson was responding to a question from the moderator of the event, who had asked what Paulson thought about the viability of maintaining sanctions against Iran, should the United States walk away from the agreement struck in Vienna last month. Congress will vote on that very question next month, but naysayers need a veto-proof, two-thirds majority in both houses to kill the deal – a formidable hurdle to clear.

In Congress and on the campaign trail, the critics of the deal – many, though not all of them Republicans – have been advocating ripping up the agreement and either leaving the U.S. sanctions in place or stepping them up to make the point to Iran and the international community that the United States means business. Some lawmakers, including Sen. Charles E. Schumer (D-N.Y.), and candidates have even suggested that the United States could force other nations into lockstep on a more hardline approach to Iran by threatening them with secondary sanctions.

Paulson thinks that idea is farfetched.

“I think it’s totally unrealistic to believe that if we backed out of this deal that the multilateral sanctions would stay in place,” Paulson said. “I’m just trying to envision us sanctioning European banks or enforcing them, or Japanese banks, or big Chinese banks.”

Sanctions against Iran have become far more extensive since Paulson left office. And Paulson’s comments, delivered in a resort city in Colorado, may not carry that much weight among his GOP colleagues in Washington.

The former Goldman Sachs chief executive came to the Treasury Department in 2006 on the eve of a colossal financial crash and left as a controversial figure for the policies he spearheaded. Since leaving that post, he has broken from the mainstream GOP party line to advocate for more attention to issues like climate change.

Even others in the Bush administration probably wouldn’t agree with Paulson: His former boss, George W., advised against lifting Iran sanctions this spring.

But Iran sanctions are Paulson’s wheelhouse, and while he didn’t direct any darts toward specific politicians or give his own point-by-point assessment of the merits of the deal, Paulson’s disdain for those who think they can strike a path to a better solution than the one reached in Vienna was apparent.

“I had a seat in Washington when we dealt with a big, intractable, messy problem, where there weren’t any neat, beautiful, elegant solutions,” Paulson said. “You were deciding between doing something that was objectionable or doing nothing at all, which could even be more objectionable.

“So I don’t particularly like it when people criticize something that’s big and important that’s been done if they don’t have a better idea,” Paulson said.